4 hrs is a long time to wait before asking for help.
Can you boot into safe mode (keep tapping F8 just after first boot screen)?
If so try a system restore to a date before the problem started.
If no restore points then try a repair of XP REpair XP
in the run box, press enter and let system file checker find and replace missing / corrupt file in windows and explorer.
This will take awhile to complete and you may be asked for the CD to be in the drive if windows is not preinstalled on the hard drive.