Date: 13-06-06 14:23
I've seen this happen before. I had it happen on 2 different boxes at 2 different times.
For my boxes, the problem was something so simple that I kicked myself...the ribbon cables were bad. For whatever reason, it would hang on a reboot, and give me an error message right after the bios kicks in, as if it couldn't read the mbr, or saw a change in the cylinder sizes or how the bios is calculating the cylinders.
Simply replacing the ribbon cables solved the problem both times.
Hope this helps!