Do not give up hope!!
I had an IBM 600 PC that was running Windows NT, and when I tried to install a USB CD burner, it totally tripped and gave me the same symptom as yours.
I can't remember exactly what my tech guy did to fix it, but it was a simple fix and the PC was booting just fine within minutes.
On Windows 2000 there is a "recover to last known good configuration" option. Are you able to reach this option? If not there is a way to get to it.
Unfortunately I can't give you the specifics of my solution right away, but I'll look into my notes and see what I did to fix it.
However, do NOT prematurely wipe your hard drive or assume that all data is lost!!