[dba-Tech] SQL installation is toast

Something happened, and I have no idea what, but now neither SQL 2000
nor the Yukon beta work. I can't reinstall them, I can't un-install them
-- nothing works. Fortunately the data and master db etc. are all backed
up on schedule, so that's going to be an issue. 

I have tried everything I could think of -- reinstall, uninstall, rename
the directories and try again, install to a different location....
Nothing works. All my other software (save those tools that depend on a
SQL instance) works fine.

I should point out that I have a server running SQL 2000 and a couple of
PCs with EM etc. loaded on them, so I can still work, but this machine
is my fancy machine with a 19-inch flat monitor etc., and I'd rather
work here than on any of the dinosaurs :)

One more thing. I've been thinking it's time for another hard drive,
anyway, so I could bump the current one up a notch, and start the long
arduous re-install everything process again. 

Does anyone have any brilliant ideas how to proceed?

TIA,
Arthur