Your are on the verge of a major corruption from spyware.
There are two things to try. Both are based on a procedure to confirm that you have a full set of the original Win files.
The best is to use the Windows program disk and the first R function you come to.
This R function will provide you with a black screen and a c prompt.
type in check disk as "chkdsk"/
You will be asked for the pass word to the administrator account - if you don't have it the chkdsk progam will not run - in XP Pro. Maybe so in XP Home.
The next procedure is to use the windows "SFC" program.
Log into window and at the run command type: sfc /scandisk
Your will need the Win XP CD in the drive as it most probably will ask fpr it.
If these do not work you will need to wipe the HD clean and reinstall the windows program.
This procedur is almost inevitable (?) As I said, you most probably have major corruption and need a major overhaul