How to Fix a PC That Won't Turn On

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PC Technician
HardwareTroubleshootingFixPower

The Problem

You press the power button and the PC is completely dead—or it flashes on and off, or fans spin with no display. This guide is for no power / no POST, not a PC that boots to a black screen (that is black screen on boot).

Before You Open the Case

Laptop vs Desktop

  • Laptop: hold power 15 seconds with charger unplugged, plug charger in (LED on the brick), try power again. Remove USB hubs and dongles.
  • Desktop: check the rear PSU switch (| vs O), power cable seated on PSU and wall, and a working outlet (lamp test).

No Lights at All

Dead outlet, tripped breaker, failed power strip, or failed PSU. Try another cable you trust (kettle lead on desktops).

The Fix: Step-by-Step

Step 1: Rule Out the Display

Fans and keyboard LEDs on but "won't turn on" sometimes means no video. Connect the monitor to the GPU outputs, not motherboard HDMI (if you have a discrete GPU). See black screen on boot if LEDs stay on.

Step 2: Front Panel and Power Button (Desktop)

  1. Shut off PSU, unplug power.
  2. Check POWER SW on the motherboard header—reseat the two-pin cable from the case.
  3. Briefly short the POWER SW pins with a screwdriver (metal touches both once)—if it boots, replace the case power button or cable.

Step 3: Reseat RAM and Power Cables

  1. Unplug power.
  2. Remove and reinstall RAM sticks until they click; try one stick in the manual's primary slot.
  3. Reseat 24-pin ATX and 8-pin CPU power on the board; reseat GPU power if present.

Step 4: Clear CMOS

Remove the coin cell for five minutes or use the CLR_CMOS jumper per the motherboard manual. Fixes boot loops after a bad overclock or BIOS setting.

Step 5: Minimal Boot (Disconnect Everything)

Unplug all SATA/USB except boot drive, remove extra RAM, GPU (use CPU graphics if the CPU has iGPU), and non-essential cards. Add parts back one at a time.

Step 6: PSU Test

Paperclip test (ATX PSU only, with caution): with PSU unplugged, bridge PS_ON to ground on the 24-pin connector—fan should spin. No spin → replace PSU. Spare PSU swap is the fastest proof on desktops.

Step 7: Laptop-Specific

  • Charger LED off → bad adapter or DC jack.
  • Blinking battery LED → leave on charge 30 minutes; swollen battery must be replaced by a shop.
  • No response after spill → power off, do not charge; professional cleaning required.

Beeps, Debug LEDs, or Brief Spin-Up

| Sign | Likely cause | |------|----------------| | One beep, no display | RAM or GPU | | Power on 1 sec then off | PSU overload, short, or VRM | | Q-LED CPU red | CPU power or dead CPU (rare) | | All fans, no POST | RAM training—wait 30s first boot after RAM change |

When It Is Not the PSU

Motherboard failure, dead CPU (uncommon), or GPU short pulling down the rail—minimal boot isolates this. Prebuilt PCs under warranty: document "no POST" and call support before random part swaps.

Data If You Get Power Back

If the machine eventually boots but was unstable, back up immediately—backup your PC before the next failure.

Safety

Unplug power before working inside. Do not open PSU shells. Laptops with non-removable batteries: use manufacturer service for power circuit work.