PC Power Supply (PSU) Problems
Quick Answer
This guide helps diagnose power supply issues in desktop PCs, from complete failure to boot to intermittent shutdowns and instability.
Please note: This guide is provided for informational purposes only. Any steps you choose to follow are at your own discretion and risk. If you're unsure, we recommend booking a professional diagnosis.
Quick Checks
Try these fast checks first — they solve most cases.
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Check power cable
Ensure the mains cable is firmly connected to the PSU and wall outlet.
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Test the wall outlet
Plug another device into the same outlet to verify it works.
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Check PSU switch
Ensure the PSU power switch on the back is in the ON position.
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Listen for fan spin on startup
If PSU fan does not spin at all, the PSU may be dead.
Guided Troubleshooting
Answer these questions to narrow down the issue.
Does the PC show any sign of life when pressing power?
Does the PC shut down randomly under load?
Do you smell burning from the PSU area?
Possible Causes
Faulty power cable
CommonDamaged or loose mains cables prevent power delivery.
PSU failure
CommonCapacitors and components inside PSUs degrade over time.
Insufficient wattage
ModerateUpgraded GPU or CPU may exceed PSU capacity.
Faulty PSU switch
Less CommonThe rear switch can fail or have poor contact.
Overheating PSU
ModerateDust buildup or poor ventilation causes PSU to overheat and shut down.
Damaged internal cables
Less CommonModular PSU cables can become damaged or loose.
If the cause requires professional attention, see Get Desktop PC wont turn on fixed.
Self-Fix Instructions
Safe steps you can try at home.
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Paperclip test
1. Unplug PSU from all components. 2. Find the 24-pin motherboard connector. 3. Bridge the green wire (PS_ON) to any black wire (ground) with a paperclip. 4. Plug PSU into wall and switch on. 5. If fan spins, PSU has basic power. If not, PSU is dead.
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Check all internal connections
1. Power off and unplug. 2. Reseat the 24-pin motherboard connector. 3. Reseat the 4/8-pin CPU power connector. 4. Check GPU power connectors. 5. Ensure all modular cables are firmly connected at both ends.
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Test with minimal components
1. Disconnect everything except CPU, one RAM stick, and motherboard power. 2. Try to boot. 3. If it works, add components back one at a time. 4. This isolates which component is causing the issue.
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Calculate power requirements
1. Use an online PSU calculator. 2. Add up all component power draws. 3. Add 100-200W headroom. 4. If your current PSU is below this, upgrade. 5. Choose 80 PLUS Bronze or Gold rated units.
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Replace the PSU
1. Purchase a PSU with adequate wattage and good rating. 2. Power off and unplug the PC. 3. Disconnect all PSU cables from components. 4. Remove old PSU from case. 5. Install new PSU and reconnect all cables.
Safety Warnings
- Never open a PSU. Internal capacitors hold dangerous charge even when unplugged.
- If you smell burning, unplug the PC immediately and do not use it.
- A failing PSU can damage other components. Replace promptly if issues are confirmed.
- Always use the cables that came with your PSU. Do not mix cables between different PSU models.
For a desktop with no power or a suspected PSU fault, start outside the case: confirm the mains cable, wall outlet and PSU rear switch, then note whether any fans or lights appear and whether shutdowns happen mainly under load. Burning smell or smoke is a stop condition, not a reason for more testing.
Safe PSU checks before deeper diagnosis
- 01Reseat the mains power cable at the desktop and wall outlet.
- 02Test the wall outlet with another device and check that the PSU rear switch is in its normal on position.
- 03Press the power button once and note whether fans, lights or other signs of power appear.
- 04If the desktop starts but shuts down, note whether the shutdown happens mainly during heavier use or also while idle.
- 05If the no-power fault began after a major hardware upgrade, record what changed so the system's power requirements can be checked during diagnosis.
Does a dead desktop prove the PSU has failed?
No. A completely dead desktop can still have causes outside the power supply, so the PSU should not be condemned from the symptom alone. One possibility is the external cable or outlet; another is a fault elsewhere in the system power path. We would confirm PSU power delivery with safe diagnostic equipment before recommending replacement.
PC no-power and PSU questions
Never open a power supply unit
The existing guide warns that a PSU can retain dangerous electrical charge even when unplugged. If you smell burning or see smoke, disconnect mains power and do not continue testing the computer.
When troubleshooting isn't enough
If these steps didn't resolve the issue, a professional diagnosis can identify the root cause.
Still need help? FixFix Labs repairs devices in Luton.
Walk in to 159 Marsh Road, Luton, LU3 2QL — or book a slot online. Same-day service on most common repairs.
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