Ive been having a few problems with my P4 3 Gig Pent with 1 Gig Ram was fine when i got nice and fast, now the CPU seems to be working hard when nothing is running, its fine till you run something, it looks like it dosent release it after the program is closed, before you could have many programs running before.
You have probably got some spyware installed, search this forum for spyware removal, you may also have some heavy load background proccess running such as a dc client, or kazaa etc? or even norton ghost or the likes, if you do a cad (ctrl alt del) and look in the proccesses section you will see what is eating up your cpu