Are all the relevant Services running, see if any are hanging in that they are set to start Automatically but have not actually started.
Try running ChkDsk to check your drive for errors. Right-click your Drive icon/ Properties/ Tools/ Error Checking. Try it first by not checking either box (this will run it in a Read-only mode) to see if it flags any hard drive or file problems. If it does, restart it by ticking both boxes, and rerun it to allow it to attempt to fix any found problems.
Run the System File Checker program from the Run Box by typing.....Sfc /Scannow in it and have your XP CD handy.
Are there any clues in your Event Viewer, or any errors in the Device Manager?