How to Fix Prime95 Crashing or Shutting Down PC (PSU Fix)
If Prime95 instantly shuts down or restarts your PC, many people panic and assume expensive hardware has failed and needs replacement. In a lot of cases, the Power Supply Unit (PSU) is simply struggling under the extreme power load that Prime95 creates, especially during Small FFT tests.
The good news is that many PSU-related shutdown issues can be fixed without replacing hardware. Below, we’ll show how to properly diagnose the PSU, what fixes to try first, and when a PSU replacement is actually necessary.
Why a Weak PSU Can Fail Prime95
Common Signs
- PC restarts or shuts off as soon as Prime95 starts
- Kernel-Power 41 error appears in Windows Event Viewer
- 12V reading drops below 11.4V in HWiNFO64 during the test
- PC runs fine for browsing or gaming but fails under Prime95
- PSU is 7+ years old or from a cheap brand
- No overheating, but stress testing stops abruptly
Troubleshooting Steps (Follow in Order)
Open HWiNFO64 and start a short Prime95 Small FFT test. Watch the 12V rail. If it drops below 11.4V or jumps around, the PSU is weak.
Open Windows Event Viewer. Go to Windows Logs, then System. Look for Kernel-Power 41 errors that match your crash times. These mean the PC lost power, not crashed due to software.
Reset the CPU and motherboard power cables firmly. A loose CPU power cable acts just like a weak PSU under load.
Check your PSU wattage on the label. Then add your CPU and GPU power use. If the total is close to your PSU rating, it is unsafe, and the PSU may struggle.
Example: CPU 100W added to GPU 250W is 350W. So the safe PSU wattage is 550W (just an estimate, you should add more headroom for stability, but anything below 400W is unsafe).
If you have a spare PSU, test it. If Prime95 becomes stable, the original PSU is likely faulty.
If the PSU is very old, low quality, or shows repeated voltage instability, replacement is usually required for stable operation.
This helps rule out power-related instability when CPU and RAM appear stable
Also, check out other guides as well for completely safe stress testing on PCs with Prime95.
Conclusion
Just check the temperature monitoring tool or look at Event Viewer for Kernel-Power 41 to see if the Prime95 issue is actually due to an inadequate power supply unit. It’s crucial to replace the PSU if HWiNFO64 shows 12V dropping below ~11.4V under load. A good PSU protects every other part of your PC, so fixing this first usually saves time and money down the road.
