Hard Drive Problem? I am stumped.

I have a Compaq Desktop that I hardly ever use. It sits running. I only
have one visual basic billing program that I periodically use. This
morning I went to boot it and got an error message that the file windows
2000 root\system32\ntoskrnl.exe was corrupted and needed to be
reinstalled. I booted off of the Win2K CD and tried to repair the disk
with no luck. I believe and I/O error message accompanied this. So i
decided to take the pc apart to clean out all dust, make sure all cables
are seated, no dust in the contacts, etc and then went to reboot. Well
now, I get no image on the monitor and the CD sounds like it is spinning
up and getting warm but all I get is 2 beeps. I have retraced my steps,
thinking that I reassembled the cables incorrectly but I do not think
so. I am not sure. There is a separate cable going to the HD, the CDR
and the floppy drive. is this correct. Then each gets power and the CDR
gets some smaller connectors. i am stumped. I am more of a Mac person so
I do not really understand how PCs go together as well. I do know that
the cable that goes from the board to the floppy is of a unique size and
cannot have been switched by accident. That leaves the CDR and Hard
Drive. If anyone can figure out what I may have screwed up, please let
me know. BTW, I had a couple of spare HD lying around and tried both of
them with the same 2 beeps. I just need to get it running so I can
contact Western Digital and see where I go from here. Please help if
you can.

This error can result from a wide range of problems. If you
are lucky, the file really is simply missing or corrupt; however, the normal
repair functions you have tried should replace it.

Probably the second most common cause for this error is disk or MBR errors.
If you have not installed the Recovery Console, boot to the Win2k CD ROM and
run Recovery Console from there. If you are able to log onto the WINNT
installation, run chkdsk, fixboot, and fixmbr.

The following is for XP, but Win2k is basically the same:

http://support.microsoft.com/defau [...] -us;314058