It might be because of insufficient memory on your computer or that you are running too many processes at the same time.
Try ALT + CNTRL + DELETE, click on process and if you have more than 45 processes.. try closing a few windows on your desktop.
If that doesn't work, it might be because you have a lot of spyware and hidden attributes that were placed in your folders by certain websites. You can download
http://www.download.com/Ad-Aware-SE-...bj=dl&tag=top5 to delete all of those bad folders on your computer and it might help it run a little faster.
After you download that and let it check your system, you should go to:
Tools > Internet Options > Clear History
Then, you can Delete Files.
That always helps my system! I hope it works for ya.