Prime95 is a great freeware tool for stress testing your CPU, allowing you to check the stability of your system under load. This can be used when troubleshooting some errors on your PC or when you want to test the results of overclocking. You can download the 32-bit of 64-bit of Prime95 from the following link: http://www.mersenne.org/freesoft/ Once you have downloaded the zip file, extract prime95.exe to a folder on your computer and run the application. The first time it runs, click the Just Stress Testing button - as this skips an optional signup process: You will then be presented with a screen where you can select the type of testing to be performed (for most CPU testing, you will want to select the Small FFT option). Be sure to enter the number of CPU cores you have in the test threads box, to make sure all of your processor gets tested. Once you are done, click OK to begin the test. If you are testing system stability, it is recommended that your leave the system running for 10-12 hours. Although most errors (if any), will show up much earlier than this. It is also worth keeping some temperature monitoring software running, to ensure that you can detect any overheating.