I've seen something very similar on a Windows 2000 Pro desktop.
Have you tried the Last Known Good? If that doesn't work, I think you are pretty much hooped. Try a System Recovery from the OS disk. You might want to get the hardware examined as well.
On the system I saw this happen on, the power supply was on its last legs. Must have lost power at precisely the wrong moment and corrupted the registry. Damage was bad enough that I had to reinstall the OS for him. Nothing else did any good.
Mind you, if you are a genius with the registry, there are linux-based tools that allow offline registry editing of NT systems... you could always rebuild the registry.