A PC that won't turn on is one of the most alarming things that can happen to a computer, but it's not always serious. Most cases come down to a loose cable, a blown fuse, or a small hardware fault you can fix at home. This guide walks you through the most common causes in order of likelihood, so you can find the problem without replacing parts you don't need to.
Start with the power supply
The power supply unit (PSU) is the first place to check. A dead PSU is one of the most common reasons a PC won't turn on at all, and it's often mistaken for a motherboard failure. Before you open the case, check these three things first.
- The power cable is seated firmly at both the wall and the back of the PC.
- The power board or surge protector isn't the problem. Plug the PC directly into a wall outlet and try again.
- The fuse in the power cable plug hasn't blown. In Australia, standard kettle-lead plugs carry a 10-amp fuse you can replace for under $5.
If the PC still doesn't respond, check whether any lights appear on the motherboard when power is connected. A faint LED on the board means the PSU is delivering standby power. No light at all points to a dead PSU or a wiring fault between the outlet and the board.
Check the power button connection
The power button on a desktop PC connects to the motherboard via a small two-pin header. These connectors come loose more often than people expect, especially in PCs that have been moved or had work done inside. Open the side panel, locate the front-panel header on the motherboard (usually labelled "PWR SW"), and reseat the connector. Your motherboard manual will show the exact pin location if you're unsure.
A quick test: short the two power pins directly with a screwdriver blade. If the PC starts, the button itself is faulty rather than the motherboard.
Reseat the RAM
Loose RAM is a surprisingly common cause of a PC that powers on (fans spin, lights appear) but produces no display and fails to boot. Remove each stick, clean the gold contacts with a dry eraser, and push them firmly back into their slots until both retaining clips snap closed. Try booting with just one stick at a time if you have more than two.
If the PC now shows the BIOS screen, the RAM was the culprit. It's worth also checking that the sticks are installed in the correct slots for dual-channel operation, usually slots 2 and 4, as described in your motherboard manual.
Isolate the display
Some PCs appear dead when it's actually the monitor that has failed. If you hear fans or see LED activity, plug the monitor into a different port (try HDMI instead of DisplayPort, or the integrated graphics port on the motherboard instead of the GPU). Try a different cable. Try a different screen entirely. It sounds obvious, but a working PC with a dead monitor is an easy thing to misread as a boot failure.
Disconnect external peripherals
A faulty USB device, a problematic external drive, or even a connected game controller can prevent a PC from posting (the initial hardware check on startup). Unplug everything except the keyboard and monitor, then try to boot. If that works, reconnect devices one at a time to identify the culprit.
Check for POST beep codes
If your PC has a speaker connected to the motherboard header, listen for beep codes when you press the power button. One short beep generally means a successful POST. Repeated or long beeps indicate a hardware fault: RAM errors, GPU faults, or CPU problems depending on the pattern. The exact code meanings vary by BIOS manufacturer, so look up your motherboard's make and model alongside the beep sequence you're hearing.
No speaker fitted? Some boards have a small onboard buzzer, and some modern motherboards include a two-digit POST code display on the board itself. That two-digit number is a direct pointer to what failed.
Inspect for physical damage
With the side panel off, look closely at the motherboard for bulging or leaking capacitors (cylindrical components that should have flat tops), scorch marks, or anything that looks burned. Smell matters here too. A sharp burning smell points to a component that overheated, and continuing to power on a board with visible damage can cause wider failures. If you see scorch marks on the PSU, replace it before attempting anything else.
Overheating from a previous session can also trigger a protection shutdown that looks identical to a dead PC. If the machine was running hot before it stopped responding, check that the CPU cooler fan is spinning freely and that the heatsink is seated firmly. For more on that, see our guide to laptop overheating causes, warning signs and solutions, which covers many of the same thermal principles that apply to desktops.
Try a CMOS reset
A corrupted BIOS setting can prevent a PC from starting. Resetting the CMOS clears the BIOS back to factory defaults. Find the round coin-cell battery on the motherboard (usually a CR2032), remove it for 30 seconds with the PC unplugged, then replace it. Alternatively, some boards have a dedicated CMOS reset jumper or button. This won't fix hardware faults, but it can resolve boot loops caused by a bad overclock or a failed BIOS update.
When to call a technician
If you've worked through every step above and the PC still won't turn on, the fault is likely inside the PSU, the motherboard, or the CPU. These are components that require proper testing equipment to diagnose accurately, and replacing a motherboard involves removing and reinstalling most of the system's other components. At that point, a professional repair is usually faster and cheaper than guessing. Our article on how much computer repair costs in Australia gives a realistic picture of what to expect before you book a technician.
One thing worth doing before the repair: if the drive itself is healthy, your data is almost certainly intact even when the PC won't post. A technician can often pull the drive and confirm this straight away. It's worth asking about this explicitly when you bring the machine in.
And if you experience a blue screen of death once your PC is back up and running, that's a separate category of problem with its own set of causes and fixes.