puter problems, big time

Don't know where to start, other than after a few days with the new service pac installed, I started having problems with windows not wanting to load or start up. Now, I can't use or read mail, can't get on the web, don't even have "my computer" on my puter! I have been using avg every nite, and ad-aware twice a month at least--saw no problems. So here I am, on vacation and no puter, whaaaaa! What kind of vacation is this?

I removed the service pac, no difference, can't do a run comand, can't dowload another virus checker. Any advice here? XP home.