Had a power issue today. Server was down for a good 4 hours. When power was restored, I found I could not log into the MySQL database as root. All the other users appeared to be okay. Just root got corrupted (either that or it was compromised before the power cut O.o ). Is that normal? I've never known just the root password to get effed.

It could.
Linux uses as much ram as it can as a buffer, so if files where modified, in the buffer, but not commited, you can loose the changes.

But it's not very probable, as almost every linux distro released in the last 5 years should use a journaled filesystem, which most promoted usage is that in case of a dirty shutdown, the journal is still there to be commited upon the next partition mount (ie: restart of the system).

Either you have someone that changed it, or you typed it wrong.
But the method to reset that password is well known, as long as you have a shell access to the server:
http://dev.mysql.com/doc/refman/5.0/...rmissions.html

Thanks buddy. Resetting it wasn't a problem.

While its possible ( as noted above )

I wouldnt let it be...
Check you haven't been hacked. check your code and make sure your tables haven't been changed.

I have had a good nose through, and can't see anything out of the ordinary. I have it all backed up anyway, so should be okay.