Ummmmm, maybe I should run a virus program, if this computer was any slower, I could deliver this post personally to you, and still beat it.
Could be you have tons of spyware bogging down your computer, too. Let it run during the day or overnight until it has completed (spyware and virus check).
Also, a cheapest way to upgrade and increase performance is to add more memory.
Also, run disk defragmeter under: start...programs...accessories...system tools...Disk Defragmenter.
This takes a while too but will speed up your system if you haven't run it for a while.
Good luck.