Computer won't turn on or black screen: what to do

The short answer: First work out what exactly is happening. If the computer does nothing at all — no LED, no fan — the problem is in the power path: socket, cable, adapter, power supply. If the fans spin up but no image appears, check the monitor and its cable, then the RAM. And if you see the manufacturer’s logo or Windows and only then get a black screen or an endless spinner, the drive is usually involved — and your data with it. At that point stop hitting the power button over and over: every extra start-up damages a dying drive further. Work through the steps below in the order given; the moment you hit a symptom of a failing drive, home diagnostics ends and the real question becomes how much the data inside is worth.

„The computer won’t turn on" is a single sentence hiding three completely different faults — and each one is fixed differently. This text is a step-by-step process of elimination, ordered from the cheapest checks to the ones that need a repair shop. Above all, it says clearly where to stop: some black screens aren’t a computer problem at all, but a problem with the drive holding your photos, your accounts or your projects.

Three different situations people describe the same way

Before you take anything apart, place your case in the right category. It saves hours of blind guesswork.

The first two rows are hardware around the computer; the last three already reach into the system and the drive. The steps below go from top to bottom.

Step 1: power — socket, cable, power supply

It sounds trivial, but a significant share of the „dead" computers people bring in have a fault outside the case.

• Try a different socket and skip the extension lead and surge protector — both can fail on their own.
• Seat the power cable at both ends. On a desktop, also check the rocker switch on the back of the power supply.
• On a laptop, watch the charging LED. If it doesn’t light up when you plug the adapter in, inspect the connector (bent pin, wobbly socket) and the adapter itself — a damaged cable near the plug is a classic.
• On newer laptops, watch what you’re charging with. USB-C charging has spread so widely that adapters get swapped around routinely — except they aren’t interchangeable. A weak phone charger may not wake a machine with a flat battery, and not every USB-C port on a laptop can accept power. Try the original adapter and the port the manufacturer marks as the charging one.
• Try a „power drain": disconnect the power (and the battery too, on a laptop with a removable one) and hold the power button for 15–30 seconds. Residual charge and a stuck state in the power circuitry are a surprisingly common reason a machine „died" overnight — and this often brings it back.

If a desktop still does nothing after all this, the power supply or the board is next — and that’s a job for a repair shop with measuring equipment. Don’t open a power supply at home; the capacitors hold voltage even after it’s unplugged from the mains.

Step 2: monitor, cable and video output

When the fans are running but there’s no image, first rule out everything that isn’t the computer.

• Check the input selected on the monitor (HDMI/DisplayPort) and the brightness — brightness knocked down to zero by accident does happen.
• Swap the cable or the port. A faulty HDMI cable behaves exactly like this.
• On a desktop with a dedicated graphics card, make sure the cable is in the graphics card, not in the motherboard connector — and try it the other way round too if the processor has integrated graphics.
• On a laptop, connect an external monitor and switch the output (Win+P on Windows). If the external image works, the fault is the display, the backlight or the display cable — not the computer. If you shine a lamp on the dark display and can faintly see content, it’s the backlight.

Step 3: RAM and everything that can be unplugged

A computer that spins up but doesn’t beep and doesn’t even show a logo has often been stopped by memory or a peripheral.

• Unplug everything except the monitor and keyboard: USB flash drives, card readers, docking stations, external drives. A computer can hang while trying to boot from connected media.
• Reseat the RAM. Turn the computer off and unplug it, pop the modules out and push them back until the clips snap shut. It also helps to try one module on its own and to swap slots — that way you isolate a faulty module or slot by elimination. In slim laptops the RAM is often soldered, so this step doesn’t apply.
• Listen and look. Beeps and blinking diagnostic LEDs aren’t a fault, they’re a code — the number and rhythm of beeps or flashes is in the manual for the board or laptop, and usually points to RAM, graphics or the board. Counting beeps on a new build makes little sense, though: a small speaker is no longer standard in cases, and boards have replaced it with LEDs next to the socket (CPU / DRAM / VGA / BOOT), while on laptops the code is often hidden in the blinking of the power LED or Caps Lock. So silence doesn’t mean the board isn’t reporting anything — it’s just reporting it somewhere else.

Step 4: BIOS, the board and black screens after an update

If the computer stopped starting after a change in the BIOS, after a power cut during an update, or after the coin cell battery went flat, resetting the BIOS to defaults can help (removing the coin cell or using the jumper on the board; on laptops, the manufacturer’s service procedure).

One important warning: a BIOS reset, Secure Boot changes or a board replacement can wake up BitLocker — Windows then asks for a 48-digit recovery key instead of letting you log in. Before you start experimenting in the BIOS, make sure you have that key. Where to find it and why it happens is covered in the article on why BitLocker suddenly asks for a recovery key.

This scenario has become far more common over the past year. Windows 10 support ended on 14 October 2025, and a large share of machines have moved to Windows 11 since — which also meant turning on TPM and Secure Boot in the BIOS, because Windows 11 won’t start without them. On top of that, drive encryption on Windows 11 often switches itself on without anyone consciously deciding to. We see the result in the shop over and over: someone goes into the BIOS because of a black screen and, instead of their system, gets a request for a key they had no idea existed. So look for the key before you change anything in the BIOS — not afterwards.

A black screen after a Windows update with a working mouse cursor is usually a graphics driver or a service rather than hardware — there it makes sense to try safe mode. But if the computer keeps cycling through automatic repair after an update, read on — that’s the chapter about the drive.

When the board doesn’t respond even with a verified power supply and memory, economics decide: on an older machine, repairing the board may not be worth it. For guidance on when to repair and when to replace, see when a laptop repair is worth it.

How to tell it’s the drive — and that your data is at risk

This is the most important part of the article. The following symptoms mean the computer itself works but is getting stuck on the drive:

• The manufacturer’s logo goes by and then you get a message like „No bootable device", „Boot Device Not Found", or the blue screen „Inaccessible Boot Device".
• The Windows loading spinner turns forever, or the system repeatedly drops into „Preparing Automatic Repair" and the loop never finishes.
• The drive isn’t visible in the BIOS/UEFI, or it disappears and reappears.
• The computer makes a regular clicking or tapping sound. That’s a mechanical head failure — switch it off immediately and don’t turn it back on. Exactly what to do and what to avoid is covered in our first-aid guide for when a drive clicks.
• The computer had been slowing down for weeks, freezing on large files or reporting read errors. A dying drive announces itself in advance — the guide how to tell a drive is dying shows how to read those signals from the SMART table.

One distinction is worth emphasising, because people get caught out by it regularly. A platter drive fails loudly and with warning: it rattles, clicks, slows down, and SMART shows growing read errors and reallocated sectors — the warning comes days or weeks ahead. An SSD fails silently and all at once: no sound, the machine seemed fine the day before, and in the morning the drive simply isn’t in the BIOS. And because new laptops and builds today are without exception based on NVMe SSDs, with no platter drive inside, silence in the case doesn’t rule the drive out as a suspect — quite the opposite. Silence took away the one warning you could actually hear.

Here’s why you need to stop trying: a mechanically failing hard drive takes more damage with every further spin-up of the platters — damaged heads tap against the surface and destroy the tracks holding your data. On an SSD, the firmware can fail in a way that makes the drive stop communicating entirely after further attempts. And repeatedly running „automatic repair", CHKDSK or a Windows reinstall on a suspect drive writes to exactly the place you’d need to recover the data from.

So if the computer won’t start because of the drive and that drive holds the only copies of something important, don’t focus on repairing the computer first — focus on recovering the data. Drive diagnostics in our lab is free of charge, and we work on a no recovery, no fee basis — if the data can’t be recovered, you don’t pay.

When to stop trying and hand it over

Home diagnostics has clear limits. Handing the machine to a repair shop makes sense when:

1. you’ve been through the power, the monitor and the RAM and the machine still doesn’t respond — from here on, the power supply and board need to be measured;
2. any symptom of a failing drive from the previous chapter has appeared and you don’t have a fresh backup — every further attempt lowers the chances for your data;
3. the computer was spilled on, dropped or hit by a storm — there, switching it on again deepens the damage to the board;
4. you can smell burning or hear crackling from the computer — unplug it from the mains immediately.

To find the fault we offer hardware problem diagnostics — we go through the power supply, board, memory, drive and graphics and tell you exactly what failed and what the repair will cost. Diagnostics is free when the repair goes ahead; if it doesn’t, PC and laptop diagnostics starts at 600 CZK. You can book directly through PC and laptop repair in Brno, or just write to us describing what’s wrong.

What to tell the repair shop up front

A good description shortens the diagnosis and therefore the price. Have ready:

• what exactly you see — no reaction vs. fans without an image vs. black screen after the logo (per the table above);
• what happened before it — an update, a storm, a drop, a move, cleaning, new hardware;
• what you’ve already tried and in what order — above all whether automatic repair, CHKDSK or a reinstall ran;
• whether you have a backup and how old it is — the decision on whether the drive may be touched at all rests on that;
• the BitLocker recovery key, if the drive is encrypted.

One last piece of advice: once the computer comes back from the shop, don’t put backups off until „sometime". A black screen the machine recovered from is a free warning — next time it may be a drive that doesn’t recover.

Frequently asked questions

The fans are spinning, the screen is black. What should I try first?

The monitor’s input and cable, then an external monitor (on a laptop), then unplug all USB peripherals and reseat the RAM. Only if none of that helps is it the board, the graphics or the drive — and that belongs to professional diagnostics.

Does holding the power button help?

Often, yes. Disconnect the power and hold the button for 15–30 seconds — this drains the residual charge and resets a stuck state in the power circuitry. It’s a safe step that can’t break anything, and on machines that „died overnight" it’s one of the most successful.

I have a black screen after a Windows update. Is the drive faulty?

Not necessarily. A black screen with a working cursor is usually a graphics driver or software, and safe mode is the way to deal with it. But if the system cycles through automatic repair or reports „Inaccessible Boot Device", the drive is the suspect — and at that point stop repeating start-ups and repairs until you know where the data stands.

How do I recognise a faulty power supply?

At home, only indirectly: the computer doesn’t respond in a verified socket with a verified cable, and the power-button drain didn’t help. Only measurement under load in a repair shop confirms the power supply reliably. Never open a power supply — the capacitors are charged.

When does a black screen mean a drive problem?

When the machine stops only after the manufacturer’s logo: a missing boot device message, an endless spinner, an automatic repair loop, a drive invisible in the BIOS, or clicking. With an SSD, though, don’t expect clicking — there the first and only symptom is usually the drive vanishing from the BIOS. At that point every further power-on has a price — with a mechanical fault, literally. Switch the drive off and have it diagnosed; with us, data recovery diagnostics is free.