PC Won't Turn On: Complete Diagnosis Guide from Power to POST

Quick Answer

If your PC won't turn on, work through it in order: confirm wall power, check the PSU switch and front-panel cables, reseat RAM and the GPU, then verify the CPU power 8-pin is plugged in. Most "dead" PCs are a loose 24-pin or unplugged EPS cable, not a fried board.

Power Path: Wall to PSU to Switch

Plug a phone charger into the wall socket to confirm power, especially during load shedding swap-overs where a tripped breaker is easy to miss. Check the PSU's rear toggle is on the "I" side. Try a different IEC kettle cord (these fail surprisingly often). If the PSU has a self-test button, hold it, the fan should spin briefly. No spin means a dead PSU or a tripped over-current protection, unplug everything from the PSU, wait 30 seconds, and retry.

Front Panel and Motherboard Standby Lights

Open the side panel and check for a small standby LED on the motherboard near the 24-pin connector, this means the board is getting power but not booting. Reseat the front-panel power switch lead (often a tiny 2-pin labeled PWR_SW). To rule out a faulty case button, briefly bridge the two PWR_SW pins with a flat screwdriver tip, if the system fires up, the case button is the problem.

POST Path: RAM, GPU, and CPU Power

Reseat the GPU firmly, then RAM (start with one stick in slot A2). Check the 8-pin or 8+4 EPS CPU power cable is fully home at the top-left of the board, this is the single most missed cable in DIY builds. If the system powers on but no display, watch the motherboard's debug LEDs (CPU, DRAM, VGA, BOOT). A solid DRAM light = failed memory training, clear CMOS and try one stick.

Frequently Asked Questions

What do I need to know about diagnosing a PC that won't turn on?

Work outward from the power source: wall, cord, PSU, motherboard, peripherals. Don't swap parts before confirming basics. Keep a cheap PSU tester or a paperclip handy, jumping the green PS_ON pin to ground tells you in seconds whether the PSU itself is dead.

What are common mistakes when troubleshooting a PC that won't POST?

Pulling parts before checking debug LEDs, and assuming load shedding damage when the real cause is a tripped multiplug breaker. Another classic: a half-seated GPU after moving the PC, the slot retainer feels clipped but the contacts aren't fully home.

Do I need special tools or parts in SA to diagnose this?

A flat screwdriver, a known-good IEC cord, and a cheap PSU tester (around R250 to R400). If diagnosis points to a dead PSU or board, full builds and components ship countrywide from Evetech with ZAR pricing and 2 to 4 day courier delivery. A pure sine wave UPS is the long-term fix for load-shedding no-boot incidents.