Sometimes its possible to have memory corruption that gets written to the HDD and when that happens usually an uninstall and reinstall of the affected software will resolve the problem.
Unfortunately with explorer you will have corruption with Windows System files.
Heres my suggestion;
First you need to test your memory with a program like Memtest86 to make sure its solid and running with no errors, if you fix this problem but still have memory errors you're wasting your time so you need to make sure memory is not an issue before repairing the problem.
You can download Memtest86 from
here under the memory header.
The downloaded file is a Floppy Bootdisk creator, find the downloaded file double click it to execute the creator program, put a blank floppy disk in your floppy drive, and the disk creator will write the boot information to the floppy.
Then set the CMOS to boot from the floppy drive boot the machine with the floppy disk you created and Memtest86 will automatically start running if it completes the 7 passes with no errors you can rule out memory as a problem and continue with the repair you'll need to do.
You can press [I believe it is the ESC key] to exit Memtest86 anytime during its running.
Then if you have no memory errors you can repair WinXP by using your WinXP installation CD.
Do a normal boot like you're installing WinXP from scratch, after you pass the F8 agreement screen, the setup will scan your HDD for previous versions of WindowsXP, it will find your previous setup and give you the option to continue installing, or press R to repair the existing XP installation.
Press R at this point and the repair will begin, it will seem like its installing from scratch because you'll have to re-enter the product key code, but when the installation is completed, all your settings, programs, files, pictures,Etc. will be there and Windows will be repaired.
Note: Do not use any repair or restore options before you get to the F8 agreement screen, or you'll end up starting over, the option is immediately after the F8 agreement.