when you computer is loaded and you are on the desktop then hold control/alt/delete together and see what is running that is eating resouces up..
4 days ago did you install any new software? or make any changes you may remember.
Have you give the registery a good clean?
Downlaod reg supreme, it is free for 30 days and cleans better than any other cleaner. run it in deep mode. clean all it finds. Once it has run and shows you what it has found, lok at the top click select then click all, this will highlight then all then at the bottom click FIX. You will get a box pop up this is for the backup of what it deletes incase you need to repair what it has done. I ahve never had a problem with it and i have used it since it came out.
http://www.macecraft.com/downloads/ reg supreme 1.1