They are designed to lock up to teach you patience. :-) :-)
twoplanekid answered it well.
I'ts like asking "Why do cars stop working?"
There are a million reasons why computers give problems, but the first thing to do is to check to see if it is a hardware problem, or a software problem. Software problems require patience to fix, but are fixable, Some hardware problems are not worth the money to fix, like replacing the motherboard in an old laptop. Test your memory, and test your hard drive.
Wayne Sallee
Wayne@WayneSallee.com
Wayne Sallee . Com