You should have automatic updated enabled through windows. If not set it that way. A lot of times an udated will fix your problem but even if it doesn't they are important. Just click on programs and then click on the update tab, which should be at the top somewhere.

manual update for windows XP

http://update.microsoft.com/ -> browse with your internet explorer

firefox or other browser wont work

I'm up to date with microsoft updates because I manually downloaded updates and I also had microsoft updates turned on. Still have the same problem. Maybe I did something wrong during reformatting, but I don't think I did.