if you are using the original PC, you should be able to just reset the bios to default and it should work.
not much is known about the original OS, but you may have an issue with the disk.
with my hacked system, i'd sometimes just get the Joshua loading screen stuck and it wouldn't boot....if i plopped in the update disk i had,it fixed something and it would boot again.
if you have the original install disks (and you should) and the original install code, (which you should also have) you can just install the software again.
be warned, if you switch any of the hardware, the install code wont work anymore. (new hard drive etc) as it's based on the serial numbers of all the hardware.
ive called in the past to Global VR to get new install codes, but after that time, another user has called and they refused to provide a code. I e-mailed them requesting another code (failed hard drive) and they would not provide another)