Most computer errors occur due to software glitches, but recurring issues -- especially full system reboots or shutdowns -- can indicate a hardware issue. To test the central processing unit for faults or overheating, run a CPU stress testing utility. These programs run the computer much harder than day-to-day use, so if your computer is already out of warranty and works fine normally, you don't need to replace it just because of a test failure.
Intel Processor Diagnostic Tool
Designed specifically for Intel-brand processors, the Intel Processor Diagnostic Tool tests basic CPU functionality and runs a short stress test. IPDT is a good option if you don't have extensive computer knowledge or want to quickly test a new off-the-shelf computer: The tool runs automatically as soon as you open it, generates simple "Pass/Fail" results for each test and only requires a few minutes in total. On the other hand, IPDT won't work well for overclockers, as Intel specifically recommends turning off your overclock before using the tool. To run a two-hour stress test, a good way to check for overheating, open the "Tools" menu and click "Config," "Presets" and "Burn In Test." Intel also offers a bootable version of IPDT for computers that can't successfully boot into Windows.
OverClock Checking Tool (OCCT)
Despite its name, you can use OCCT to test any computer's CPU, whether or not you overclock it. The program includes has two separate CPU tests: OCCT and LINPACK. LINPACK heats up the CPU as much as possible, making it a good test of the cooling system. The OCCT test doesn't generate as much heat, but more quickly detects computational errors that can cause programs to crash or your system to freeze. Pick a test and click "On." By default, the test runs indefinitely until you click "Off." Alternatively, change the test type to "Automatic" instead of "Infinite" and enter a duration of at least an hour.
Prime95 Stress Test
Though not its primary purpose -- finding new Mersenne prime numbers -- Prime95 includes a few types of stress tests. When you first run the program, choose "Just Stress Testing" to use the test mode. The default setting, "Blend," tests both your CPU and RAM. A crash during a Blend test won't help you figure out which part has a problem, so switch to "Small FFTs," which only uses the RAM minimally. Unless Prime95 crashes or overheats your system, it runs until you open the "Test" menu and click "Stop." A few hours without a crash normally indicates a stable CPU, but to be absolutely sure, run the program for an entire day.
Dealing With Test Failures
If you overclock your CPU and fail a CPU test, turn down your overclock and run the test again until you find a stable setting. On systems without an overclock, tests can fail for two main reasons: faulty hardware and overheating. A severely overheated CPU causes the computer to turn off entirely. To fix the problem, clean out the system's fans and make sure to leave ventilation room around the system. A faulty CPU can cause error messages in the testing program, or cause the computer to crash or reboot while testing. If you also encounter these problems during regular use, you need to replace the CPU or the computer to fix the problem.
Information in this article applies to IPDT version 2, OCCT version 4 and Prime95 version 28. It may vary slightly or significantly with other versions.