Few things are more alarming than pressing your PC's power button and being met with nothing — no Windows logo, no loading screen, just a black screen and silence (or just fans spinning). This is one of the most common faults we see at PC Repair Services Edinburgh, and while it can feel catastrophic, the cause is often straightforward once you know what to look for.
This guide walks you through diagnosing a PC that won't boot, from quick checks anyone can do to signs that professional help is needed.
What Is POST and Why Does It Matter?
When you turn your PC on, the motherboard runs a self-check called POST — Power On Self Test. During POST, the system checks that essential components like RAM, GPU, and storage are working correctly. If POST fails, Windows never gets a chance to load, and you'll typically see either a black screen or an error message.
If POST passes, your PC hands over control to Windows. A black screen after the Windows logo appears is a different issue — usually a software or driver fault rather than a hardware problem.
1. Start With the Obvious Checks
Before assuming hardware failure, eliminate the easy causes:
- Is the PC actually on? Check the power button light and listen for fan movement. If there's no activity at all, check your power cable, wall socket, and any surge protector switches.
- Is the monitor working? Try a different cable (HDMI or DisplayPort), a different port on the back of the PC, or plug the monitor into another device to confirm it's receiving a signal.
- Are you plugged into the right port? If your PC has a dedicated graphics card, make sure the monitor is connected to the GPU's ports — not the motherboard's built-in video output. Plugging into the wrong socket is a surprisingly common cause of a black screen.
- Disconnect external peripherals. Unplug USB drives, external hard drives, and extra monitors. Some PCs try to boot from a USB device and fail silently when there's nothing bootable on it.
2. Listen for Beep Codes
During POST, your motherboard may emit a series of beeps if it detects a fault. Different patterns mean different things depending on your motherboard's BIOS manufacturer, but common codes include:
- One long beep, two or three short beeps — graphics card fault
- Continuous short beeps — RAM not seated properly or failed
- No beeps at all — power supply or motherboard fault
If you hear beeping, make a note of the pattern and search for your specific motherboard's beep code guide, or bring the PC to us — we can interpret the codes and identify the faulty component quickly.
3. Reseat Your RAM
Loose or improperly seated RAM is one of the most common reasons a PC refuses to POST. Over time, thermal cycling can cause memory sticks to work slightly loose in their slots.
To reseat RAM: power off the PC completely and unplug it from the wall. Open the side panel, locate the RAM sticks (long, thin green or black strips), press the clips at each end to release them, and firmly re-insert them until you hear a click. If you have two sticks, try booting with just one at a time to rule out a faulty module.
4. Check Your Graphics Card
Like RAM, a graphics card can work loose — especially in a system that's been moved or knocked. If your GPU isn't seated properly, you'll get no display output even if everything else is fine.
Reseat the card by releasing the PCIe slot clip, removing the card, and firmly pressing it back in. Also ensure the GPU's power connectors (typically 6-pin or 8-pin cables from the PSU) are fully inserted. If you have integrated graphics on your CPU, remove the dedicated GPU temporarily and connect your monitor to the motherboard's output — if the system boots, the GPU may be faulty. Our hardware upgrade and repair service covers graphics card diagnosis and replacement.
5. Is Your Storage Drive the Problem?
If POST completes successfully but Windows fails to load, your boot drive may be the culprit. You might see an error like "No bootable device found" or "Operating system not found."
First, check that your hard drive or SSD is connected properly — unplug and re-plug both the data cable (SATA or M.2) and the power connector. If the drive is making clicking sounds or grinding noises, that's a sign of physical failure and you should stop using it immediately to avoid further data loss.
A corrupted Windows installation can also prevent booting — this is often fixable with a Windows repair USB without losing your data. We cover this as part of our OS installation and repair service.
6. Reset Your BIOS / Clear the CMOS
If your system has recently had a failed BIOS update, or settings were changed that caused instability, clearing the CMOS can restore the motherboard to factory defaults. This is done by removing the small coin-cell battery on the motherboard for 30 seconds, then replacing it. Consult your motherboard's manual for the exact procedure, as some boards have a dedicated CMOS reset button.
7. Power Supply Failure
A failing power supply unit (PSU) is a less obvious culprit, but it's common — especially in older systems or those running high-powered components. Symptoms include random shutdowns, failure to power on, or fans spinning briefly before cutting out. We carry out PSU diagnosis and replacement as part of our standard repair service.
When to Call a Professional
If you've worked through the steps above and your PC still won't boot, it's time to bring it in. Motherboard faults, processor issues, and advanced data recovery from a failed boot drive all require specialist tools and experience.
We help customers across Edinburgh and the surrounding area — from Gorebridge and Loanhead in Midlothian to Livingston in West Lothian — diagnose and repair boot failures of all kinds. Most repairs are completed the same day or within 24 hours. You can drop your PC off at our workshop at 140 Parkhead Drive, Edinburgh EH11 4RX, or book a home callout if you'd prefer us to come to you.
Book a repair online or get in touch — we'll get your PC running again.