Just a thought, were you watching Bill Murray's 'Groundhog Day' just prior to shutdown? 
Seriously, if you have auto-update switched off, then you should not be getting any "configuring updates "messages. At a guess, I'd say you've picked up a nasty from somewhere and it has your PC stuck in a loop. I can't recall the name off-hand, but I do recall reading a while ago about a virus/trojan that does this to peoples PC's... may have been on C-net, PC User or some such site.
Do you dual boot with XP, Win7, perhaps? If so, you could perform viral and malware scans from there to see if Vista has indeed become infected. Also, have you tried booting from the installation disc and running Vista/performing a repair install from there, just in case it's something as simple as a missing or corrupt dll - registry setting? Other than this I'm not too sure what else you can do, given you are unable to access Vista in either normal or safe modes.
Hopefully somebody more knowledgable than I will come along and offer assistance to this issue. Anyhow, best of luck with it and I hope you're up and running again soon.
