I would still defrag your harddrive. It can take a while depending. Since you don't know how to do it, I assume it has never been done. Start it when you go to bed and it should be done by morning

Start -> Programs -> Accessories -> System Tools -> Disk Defragmentor

I am not sure but you may need to shut down any programs that might be running in the background. Only defrag SHOULD be the only program you have open...like on the task bars and stuff. Don't go crazy shutting down stuff. Just shut down everything you know about. That should be good enough