Shoutbox

Blah.. Since you didn't give any information about your computer, this could be anything..
Some examples:

Have you run diagnostics to see if your hard drive is not causing the problems?  How old is your system? Over 2 or 3 years a lot of hard drives degrade. It might be a hardware problem.

See 'System Idle Process' on Task Manager. If you are not running any programs it should hover around 97-99%. If it fluctuates much more than this you should install and update then run Spybot and Ad-aware and spywareblaster (or some programs similar to these).