Pressed the power button and got absolutely nothing — no fans, no beeps, and no motherboard lights at all? Don’t assume the worst yet. A PC that won’t turn on with no motherboard lights means the 5V standby rail from the power supply isn’t reaching the board — and in our repair workshop, the cause is a dead PSU, a tripped protection circuit, a faulty power button or even a blown plug fuse far more often than a dead motherboard. This guide walks you through the exact diagnostic order we use at the bench, from quickest check to most involved.
First, work out which “dead” you actually have
These three situations look similar but have completely different causes. This guide covers the first row — if you’re in row two or three, jump to our other guides instead.
| Symptom | What it tells you | Where to start |
|---|---|---|
| No motherboard lights, nothing responds at all | Standby power (5VSB) isn’t reaching the board. Power delivery problem: socket, cable, PSU, wiring or a short. | This guide — carry on below |
| Motherboard LED is on, but pressing power does nothing | The board has standby power but isn’t getting the “switch on” signal. Usually the case power button, front panel wiring or the board itself. | Steps 5–8 below |
| Fans spin, lights come on, but no display | The PC powers up but fails POST — RAM, GPU, CPU or monitor territory. | Our PC won’t POST troubleshooting guide |
No motherboard lights: the 9-step diagnostic in the order we do it at the bench
Rule out the wall, the lead and the extension strip
2 minutesPlug the PC directly into a wall socket you know works (test it with a lamp or phone charger). Bypass any extension strip or surge protector completely — surge protectors can trip silently after a storm and look perfectly normal while passing no power. Swap the kettle lead for another one; they’re identical to the leads on most monitors and kettles, so you almost certainly have a spare.
Check the fuse in the plug (the very British failure)
5 minutesUK three-pin plugs contain a fuse, and a PC that “died overnight” is sometimes nothing more than a failed 13A fuse in the kettle lead’s plug. Unscrew the plug (or pop the fuse carrier on moulded plugs), swap in a known-good 13A fuse — borrow one from another appliance lead if needed — and try again. While you’re there, check the lead for kinks, crush damage or scorch marks near the plug.
Do a full power drain (clears tripped PSU protection)
2 minutesModern power supplies have protection circuits (over-current, over-voltage, short-circuit) that can latch into a tripped state after a power cut, surge or fault — and while latched, the PSU plays dead. Switch the PSU rocker to off (O), unplug the mains lead, then press and hold the case power button for 30 seconds to discharge the residual power in the system. Reconnect, switch the rocker back on (I), and try the power button.
Reseat the 24-pin and the 8-pin EPS connectors
5 minutesWith the PSU off and unplugged, open the side panel and check the two power connectors that matter: the big 24-pin ATX connector on the right edge of the motherboard, and the 4/8-pin EPS CPU power connector in the top-left corner. Unclip both fully and push them back in until the latch clicks. If your PSU is modular, reseat the PSU end of each cable too. A connector that’s 95% seated is enough to kill standby power — and the top-left EPS plug is the one people forget after moving or cleaning a PC.
Bypass the case power button with a screwdriver
5 minutesCase power buttons fail more often than people expect, and a broken button looks exactly like a dead PC. Find the front panel header on the motherboard (bottom-right corner on most boards, labelled F_PANEL or JFP1), pull off the two-pin PWR_SW connector, and briefly touch both PWR_SW pins at the same time with the tip of a flat screwdriver. That momentary short is precisely what the power button does — nothing more.
Test the PSU on its own — the paperclip test
10 minutesTime to find out whether the PSU itself is alive. Unplug the 24-pin connector from the motherboard. With the PSU switched off, straighten a paperclip into a U shape and bridge the green wire (PS_ON, pin 16) to any black ground wire on the 24-pin connector. On all-black cables, count to pin 16 — most PSU manuals and Corsair’s jump test guide have a pinout diagram. Plug in, flick the rocker on, and watch the PSU fan.
This is safe and doesn’t void the warranty — shorting PS_ON to ground is literally what the motherboard does every time you press power. For a slightly better test, leave a case fan or SATA drive connected so the PSU has a small load. A £10 PSU tester does the same job with voltage readouts, and if you own a multimeter you can check the purple 5VSB wire (pin 9) against ground — it should read close to 5V the moment mains is connected, even with the PSU “off”. That purple wire is exactly the rail behind your missing motherboard lights.
Strip the system to the bare minimum
15 minutesA single shorted component anywhere in the system can drag the 5VSB rail down and leave you with no motherboard lights even though the PSU is healthy. With power disconnected, remove everything non-essential: all USB devices (including the keyboard and mouse), all drives, the graphics card, any expansion cards, all but one stick of RAM, and every cable except the 24-pin, the EPS and the CPU cooler fan. Reseat the CMOS battery (the CR2032 coin cell) while you’re in there — pop it out for a minute, then back in — or swap it for a fresh one; they cost about a pound and a flat one can prevent startup on some boards. Then try to power on.
Breadboard it — take the motherboard out of the case
30 minutesIf a stripped system still shows no life, the case itself becomes a suspect. A misplaced brass standoff, a loose screw trapped behind the board or a damp patch can short the motherboard against the case — the classic killer of new builds and recently-moved PCs. Unscrew the motherboard and sit it on its anti-static bag on top of the box it came in (a wooden table works too). Connect only the 24-pin, the EPS, CPU cooler and one RAM stick, then start it with the screwdriver trick from step 5.
While the board is out, inspect it under good light: bulged or leaking capacitors, scorch marks around the VRMs (the components near the CPU socket), a burnt-electronics smell, or bent pins in the connectors all point to hardware damage.
The definitive swap test
30 minutes + a spare PSUThe end of the line for home diagnosis: if there are still no motherboard lights, connect a known-good PSU (borrowed, spare, or a new one you can return) to the breadboarded system — just the 24-pin and EPS. If a healthy PSU still can’t wake the board, and you’ve been through steps 1–8, the verdict is in.
The 60-second decision tree
Still not sure where you stand? Run your no motherboard lights symptom through this flow:
One extra clue worth knowing: the blinking PSU light
Some power supplies have a small LED on the back. If that light blinks or flickers only while the 24-pin is connected to the motherboard, but stays solid with the board disconnected, the PSU is repeatedly hitting its short-circuit protection — which points at a short on the motherboard side rather than a bad PSU. It’s a small detail, but it can save you buying a power supply you didn’t need.
Frequently asked questions
Is the paperclip test safe?
Yes. Bridging the green PS_ON wire to ground is exactly the signal the motherboard sends when you press the power button, and it doesn’t void the PSU warranty. Just make sure the PSU is switched off while you insert the paperclip, keep fingers clear of the pins when you switch it on, and never open the PSU casing itself.
Can a power surge kill the motherboard and PSU at the same time?
Unfortunately yes. A strong surge — lightning, or a fault on your supply — can take out the PSU, motherboard, and occasionally the CPU or GPU in one hit. That’s why the swap test with a known-good PSU matters: it’s the only way to tell whether the board survived. A decent surge protector or UPS is cheap insurance, especially if your area gets storms or power cuts.
My motherboard LED is on but the PC still won’t start — same problem?
Not quite. No motherboard lights means no standby power at all, while a lit standby LED means power is reaching the board — so the PSU and cabling are largely off the hook. The usual suspects become the case power button (step 5), a shorted peripheral (step 7), or the board itself. You can skip the wall-power and fuse checks and go straight to the screwdriver test.
How much does it cost to fix a PC that won’t turn on?
It varies enormously with the cause: a plug fuse costs pence, a case power button a few pounds, a quality replacement PSU roughly £60–£120, and a motherboard replacement anywhere from £80 to several hundred plus fitting. That’s exactly why it pays to diagnose before buying parts — most “dead” PCs we see need one inexpensive fix, not a new board.
Should I try to repair a dead PSU?
No. PSU capacitors hold lethal charge even when unplugged, and a compromised PSU can damage everything it’s connected to. Replace it with a reputable unit sized for your system — and if you’re unsure what wattage you need, our PSU calculator will tell you in under a minute.
Still no motherboard lights after all nine steps?
Bring it to us. TechSavant has been diagnosing and repairing custom and pre-built PCs in Harrow since 2016 — we’ll test your PSU under real load, inspect the board at the bench, and give you an honest verdict on repair vs replace before any work starts.
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