I don't know how old your computer is.. but can you try and do a system restore from the computer? Start (button) -> Accessories -> System tools (system) -> system restore.. my 1 yr old computer (got at walmart) keeps crashing so I keep resetting it back to a former date, I just need it to last one more year through school.

Oh..and you should put AVG (virus) software on your computers. I know most people have McAfee or Norton but those don't work as well.. an IT guy told me. And, it's free..
http://www.grisoft.com/ww.download-trial
I hope this helps a little!