How do you know if your computer is bad?

Most newer drives have built-in diagnostic tests known as "SMART." In your BiOS, make sure SMART monitoring is enabled. If there is a problem with your hard drive, it will display a message when you boot up.

For older drives, or for computers that don't support SMART in their BiOS, the drive manufacturers usually have diagnostic tools you can download for free from their website. These can read the SMART status of the drive, as well as perform manual read/write tests.