What operating system are you running ?
If it's windows 2000, right click on the toolbar at the bottom of your screen and choose task manager from the popup menu. Click on the Processes tab and then on the CPU column so that the application that uses the most cpu appears at the top of the list. This will tell you what it taking up your CPU time.
Windows 98, if you CTRL+ALT+DEL, one application may appear as "not responding", that would suggest it is the culprit.
I don't run ME or XP, so don't know about those.
HTH