I'd check the hard drive first, to eliminate it as a possibility. One of the biggest causes of slow downs are failing hard drives -- outside of excess programs loading up... which doesn't sound like the issue here.
You can schedule a check disk by going to:
1) "My Computer" then right clicking your main drive.
2) Go to properties.
3) Click the tools tab.
4) Click "Check Now" under error checking.
5) Check all boxes under "Check disk options".
The check disk will be scheduled upon restart of your computer. Restart to run the check disk and write down the results.
If you see any "bad sectors" or "bad clusters", this could be a sign of a failing hard drive.
(It could also be disk thrashing if memory is going bad and the paging file is having problems, but lets start with the hard drive first).
Edited by Suicide King, 22 March 2011 - 09:54 PM.