Try to provide us with a little more description... are you doing anything in particular?
First...
try downloading a free program called EndItAll. You can get it from my clan's website (
http://www.clangdc.com) by clicking on the downloads link. (make sure your screen resolution is set for 1024x786). Once you run that program it will close all background applications which can sometimes be the cause of something locking up.
Second...
How much RAM do you have in your system. Make sure each stick is fully seated. Lack of RAM can also cause a program to stop working properly under certian conditons.
Third...
Update your video card drivers.
Hopefully that will help some.