I know it may be a pain, but if you have tried several different
drives, the BIOS finds it, and you can boot from it, it doesn't
sound like a hardware problem.

You may have to reinstall your OS, or better yet, a different
one, to see if it will fix it. Your installation may be corrupted
somehow, in which case a reinstall will fix it. Or it may be a win2k
issue, and microsoft may have a bug fix.