try reinstalling xp first if thats the os you are running.
try to do a repair install so you don't lose your data.
If it is just the os it will tell you if it can do a repair install or not.
I just went through somehting very similar.
Ended up having a couple of corrupt xp files
I could not do a repair install and ended up having to do a complete reinstall, losing any data I had not backed up.
__________________
|