How long has XP been installed on this unit?
I know it sounds silly but I've seen numerous install problems with XP and what you are describing is one of them.
The only real solution is to totally erase the HDD and start from scratch again. There are quite a lot of problems that happen with a bulk install of XP which is what Microsoft supply us dealers to cut back on time needed to build and deliver computers.
First backup any data that you have on the unit and then attempt to download a utility from Maxtor that writes zero's to every section of the HDD and build a floppy from that program and then run a Windows Boot Floppy and the place in the utility and run it to wipe the drive.
You could attempt to reinstall Windows over you're existing installation but in my experience it doesn't solve any of the problems that you originally had.
Good Luck. If you want any more info you can contact me through the "Peer Listings" and I'll attempt to help you as much as humanly possible.
Col