I was working on a ladies computer yesterday. Its a Compaq about 4 years old. When i started the PC it would lock up on the XP loading screen. There was no work around for this. I tried to do a recovery from the XP home disk. I also tried to do a recovery from the Compaq recovery system. My only option after troubleshooting for a bit was a full recovery with the Compaq System reovery disks. This completly wiped the drive and loaded everything like it was when she bought it. It appeared that everything was fine. 10 minutes after i left she said it wouldnt boot and there was a message on the screen. I went back and looked and it was at the black screen pre XP load stating that it was missing the hal.dll file. This was a fresh install.

So the skinny? drive going bad?

There's a good chance that the drive is failing. Run a drive check tool from the drive manufacturer's web site. If it's bad, replace the drive. If it tests good, then look for other hardware problems, i.e. bad RAM or bad motherboard.