I see that no one has responded to your question. I'll give it a shot...

How old is the laptop/notebook unit you are working on? Maybe it's still under warranty?

If you are continually not able to access the hard drive, it just might be DOA. With a laptop/notebook computer, it is close to impossible to check to see if everything is hooked up properly on the inside of the case. If the computer is more than a year old, it is likely the hard drive is toast (however, I had them die at less than a year old). Again, check with the manufacturer per warranty. Your story sounds a lot like a dying hard drive... You don't need to install any drivers since XP would cover that with generic drivers. Or course, there is always the outside chance that the motherboard is dying. But, don't give up yet...

Having had a recent similar problem with an internal hard drive that I made into an external one, I discovered that the operating system would not recognize my hard drive because it had not been formatted to the OS's liking, both when it was an internal hard drive and after I made it into an external hard drive. Frankly, I had to use my Vista-OS computer in order to access the messed-up hard drive and to get it formatted. For some reason, my XP-OS computer would not access this goofy hard drive.

Going back to your situation: I would assume that your ex- has the original manufacturer's recovery disk with the OS on it. Use this to boot up the computer (put the disk into the optical drive when the computer is on, then shut the computer down...and turn it back on). The computer should go right to the disk when it is turned on. Any XP-OS disk I've seen will ask if you wish to format your hard drive (i.e. the C-drive) before the setup program begins...tell it "yes." I am assuming your ex's computer is unusable as it is...like there is no operational OS on it at this point?

If you can get into the Setup program (prior to the computer booting up the OS/Windows), usually via a function key (which differs from brand to brand), find the screen that lists drives, hard drive(s) along with the CD or DVD drives. You must find the screen that tells you the sequence used to read the drives (mainly, for booting up the computer). Generally, the CD or DVD-ROM is the first drive checked, then the hard drive (C-drive). Follow the directions in the Setup screen if you have to reset the boot sequence to reflect this: the CD or DVD-ROM drive first and C-drive (hard drive) second.

Hope something I mentioned will solve your problem. In the meanwhile, lots of luck with this one. It is nice of you to offer to help out the ex-, no matter what the end result turns out to be. You know the old saying (edited a little): no good deed goes unpunished!