When a desktop won’t turn on, check power, connections, and parts in a short, safe sequence.
Your tower sits there, fans still, screen black. Skip guesswork. Follow this order. Start outside, move inward, and stop when it wakes.
Before You Start: Safety, Tools, And Clues
Unplug the power cable and press the case button for ten seconds to drain charge. Ground yourself by touching bare metal on the case. Keep a Phillips driver and a clean desk. Note the symptom: no lights at all, lights with no fans, fans with no display, or a looping start and stop.
Quick Triage: Symptoms, Likely Causes, And First Moves
| Symptom | Likely Cause | What To Try |
|---|---|---|
| No lights, no fans | Outlet, cable, switch, PSU | Wall test, new cord, PSU switch to I, new outlet |
| Lights only | Front switch lead, PSU fault | Check front panel header, bridge power pins |
| Fans spin, no display | GPU cable, RAM seat, monitor | Reseat RAM, swap video cable, new screen input |
| Starts then shuts off | Short, cooler mount, PSU trip | Check standoffs, reseat cooler, desk-boot test |
| Beep or LED code | POST error | Match pattern to maker chart and act |
Step 1: Confirm Power, Switches, And Cables
Plug the tower straight into a wall socket. Strips and UPS units hide faults. Flip the power supply switch to the I position. Try a second IEC cable. Look for a standby LED on the motherboard.
Trace the 24-pin main board lead, the 4-pin or 8-pin CPU power cable near the socket, and any GPU leads. A loose CPU cable stops boot cold. Intel calls these must-checks and notes you can bridge the board’s power switch pins to rule out a bad front button Intel power steps.
Step 2: Rule Out Display Mix-ups
Many “dead PC” calls trace to a monitor path issue. Confirm the monitor turns on and shows its logo. Pick the right input. Move the cable from the graphics card to the motherboard port only if your CPU has built-in graphics. Try a spare cable.
Step 3: Strip To Essentials And Reseat Parts
Disconnect drives, extra PCIe cards, and front USB headers. Leave the motherboard, CPU with cooler, one stick of RAM in the primary slot, and power leads. Tap the power button. If it wakes, add parts back one item per test. If it stays silent, reseat RAM and try one stick in each slot.
Step 4: Clear CMOS To Reset Firmware State
Stuck settings stop boot. Power off, unplug, and hold the case button for ten seconds. Then use the clear jumper or pull the coin cell for a minute. ASUS shows both methods and the order to follow ASUS clear CMOS. Put the cell back and try again.
Step 5: Test The Power Button Path
The case switch might be failing or miswired. Find the two power switch header pins on the board front panel block. Briefly bridge the two with a screwdriver tip. If the system starts, the board is fine and the case switch or its lead needs service.
Step 6: Try A Minimal Boot Outside The Case
A stray standoff can short the board. Set the board on its box or a wood table. Fit CPU with cooler, one RAM stick, and the PSU. Use onboard video. Bridge the power pins. If it boots there, the case build caused the short.
Step 7: Swap Known-Good Parts In This Order
Use parts you trust or borrow from a friend. Start with the power supply. Move next to RAM. Then try a different graphics card or onboard video. Leave the motherboard for last. If a part swap fixes the issue, retest the old part in a second rig.
Step 8: Signs The Power Supply Is The Culprit
No fan spin, a faint click, or a start then stop points at PSU protection. The unit may trip when rails sag. If case lights work yet the board stays dark, the 5V standby rail could be fine while main rails fail under load. A trusted spare PSU is the cleanest test.
Step 9: Cooling And CPU Checks
If the system spins up and dies in a few seconds, the cooler mount may be loose. Reseat the cooler with fresh paste. Plug the CPU fan lead into the CPU fan header; many boards halt boot if that header reads zero.
Step 10: Storage And Peripherals That Stall Boot
A shorted USB device can hold a board in reset. Unplug every stick, printer, and hub. Try again with only keyboard and mouse. Bad SATA cables and failing drives can freeze the splash screen. Boot once with all storage cables removed. If the board passes POST with no drives, a drive or cable is the cause.
Model-Specific Indicators And What They Mean
Many boards use beep or LED patterns to flag a bad part. One long and two short often points to video. Repeating single beeps often point to RAM. Some makers moved to diode patterns near the RAM slots. Check your board booklet or brand site for the table that matches your model. If the case has a two-digit POST display, note the code and look it up.
When The Desktop Won’t Turn On But Fans Spin
This state says your power path is live, yet POST fails. Reseat memory and the GPU. Test with the GPU removed and use the motherboard video port if your CPU supports it. Pull all drives. Reset CMOS. Check that the boot device shows up. If no splash screen appears, move to a minimal boot.
When The Desktop Won’t Turn On At All
No fans, no LEDs, no signs at all directs you to outlet, cord, PSU switch, and power supply. Swap the wall outlet with a lamp test. Use a known good cable. If the motherboard has a standby LED and it stays off, the PSU or the wall path is the suspect.
Major Causes And How To Confirm Each One
| Suspect | What Confirms It | Next Step |
|---|---|---|
| Power strip or outlet | Lamp test fails or works only on another socket | Use a new outlet, retire the strip |
| Front power switch | Board starts when pins are bridged | Replace or rewire the case lead |
| PSU | Known-good unit boots the rig | Replace with a rated unit |
| RAM | Boots with one stick or a different kit | Replace or RMA the bad stick |
| GPU | Board boots on onboard video | Swap GPU or service it |
| Motherboard | All other parts pass, still no POST | Replace the board |
Close Variation: Desktop Not Turning On Fixes That Work Fast
Need a quick pass? Wall test and cord swap. PSU switch to I. 24-pin and CPU 8-pin checked. Monitor input checked. RAM reseated, then single stick tested. CMOS cleared. Minimal boot on the box. Spare PSU tried.
Care For Data While You Troubleshoot
Do not keep power cycling a drive that clicks or stalls. Pull it and image it in a system. If the system boots after a drive is unplugged, that drive may be near the end. Copy files first.
Know When To Stop And Seek Service
Stop after the spare PSU and minimal boot tests if nothing changes. A shorted board or a dead CPU calls for bench gear that most homes lack. New machines under warranty should go to the seller with a neat list of steps you tried.
Prevention: Habits That Keep The Power Path Healthy
Dust blocks fans and heatsinks and raises heat. Clean the case with short air bursts. Keep the PC on a surge protector or a UPS with headroom. Route cables so GPU and CPU power leads seat fully.
Simple Order Of Operations You Can Print
Outside Checks
Wall socket test, new cord, PSU switch, unplug extras.
Inside Checks
24-pin and CPU 8-pin, GPU leads, RAM reseat, single stick.
Reset And Reduce
Clear CMOS, remove drives, boot on the desk with onboard video.
Swap
Test a spare PSU, then RAM, then GPU, then board.