Hi Rob
just my 0,02 cent worth suggestion ...
Maybe some files have been corrupted (disk failure) so you are no more able to reboot properly.
Have you tried to reboot off a knopix cd, and then try to check your hd status?
I had a couple of times a similar problem (in the very beginning, when I was making a lot of experiments and system was crashing frequently) and it ended up that the shortest fix was to reinstall pluto keeping data partition.
Obviously if you don't have a recent backup of your mysql tables this may result a bit annoying ..
Regarding backup, you may find interesting this thread
http://plutohome.com/support/phpbb2/viewtopic.php?t=565Again, just my 0,02 cent
Regards
Marco