How to Fix Prime95 BSOD or Threads Stopping: Complete Guide
If you notice Prime95 not using all cores or threads during stress testing, the problem may come from Windows or driver corruption instead of failing hardware. Prime95 depends on stable system files, chipset drivers, and Windows handling cores correctly to fully load every core and thread. When those background components stop working correctly, Prime95 may freeze, stop workers, show low CPU usage, or trigger Blue Screen errors even though temperatures and voltages look normal.
The issue is fixable; follow the steps given below for a stable system while stress testing with Prime95.
Corrupted Windows or Drivers Fix (Prime95 Not Using All Cores)
Prime95 creates an extremely heavy CPU workload, especially during Small FFT and Blend tests. Windows must constantly move these workloads across CPU threads correctly. If Windows files become corrupted or chipset drivers stop communicating properly with the processor, Prime95 can fail to use all cores or stop workers unexpectedly.
Here are common signs that usually point to driver or memory issues rather than a broken chip, and what to do next:
Common Signs
- Blue screen with codes like IRQL_NOT_LESS_OR_EQUAL or MEMORY_MANAGEMENT
- Prime95 not using all cores during a test
- Prime95 threads stop almost right after the test starts
- Random restarts while idle or under load
- Crashes only started after a Windows update or new driver install
Troubleshooting Steps
Check Prime95 Worker count
Before changing drivers or reinstalling Windows, check the thread count inside Prime95.
Open Prime95 and check the “Number of torture test threads to run” or “Number of cores to torture test” setting when starting the test. Prime95 uses one worker for each CPU thread. If this number is set too low, the program will not fully load the processor.
To find the correct number, open Windows Task Manager, go to the CPU section, and check the “Logical processors” count. Set Prime95 to the same number. For example, an 8-core CPU with Hyper-Threading or SMT enabled usually shows 16 logical processors.
Stop Windows from auto-restarting on BSOD
Press the Windows key, type sysdm.cpl, and press Enter. Go to the Advanced tab, then Settings under Startup and Recovery. Uncheck Automatically restart. This keeps the blue screen on long enough to read the error code.
Check past blue screens
Download a free tool called BlueScreenView from NirSoft. It shows a list of past BSODs and which driver or file caused each one.
Close background apps
Shut down antivirus, Windows Update, screen savers, and anything you do not need. These can interrupt Prime95 and look like hardware faults.
Unplug extra devices
Keep only your keyboard, mouse, power cable, and monitor connected. Remove USB hubs, external drives, and game controllers during testing.
Repair Windows system files
Corrupted Windows files can directly affect Prime95 stability. Open Command Prompt as Administrator and run sfc /scannow to repair damaged system files.
If Windows repeatedly finds corruption after multiple scans, the operating system itself may already be unstable enough to affect stress testing.
Restart your PC afterward.
Update drivers from the maker’s site
Next, install the latest official chipset, graphics, and network drivers from your motherboard manufacturer’s website. Chipset drivers are especially important because they control communication between Windows and the processor scheduler.
Avoid third-party driver updater tools since they often install wrong versions.
Reinstall Windows as a last step: (Optional)
Back up your files, do a clean Windows install, install only essential drivers, then run Prime95 again.
Conclusion
Most Prime95 crashes are often blamed on hardware. But when you notice Prime95 not using all cores alongside freezing, BSOD errors, worker crashes, or low CPU usage, corrupted Windows files, broken chipset drivers, incorrect thread settings, and conflicting background software could also be the cause.
Start by checking thread counts, repairing Windows files, updating official drivers, and removing unnecessary software before replacing hardware components.
