A question for the more computer savvy people out there....

My computer has been acting spazzy lately. And today, when I tried to log in to the administrators side of my PC, I got a message that said "User profile service failed the log in. User profile cannot be loaded". The guest side of the computer still works fine (I'm using it now). But I can't access anything from the admin side or do anything that requires an admin password.

So....what exactly does that mean? Is there a way to fix this (or at least get into the administrator side via a "back door")?
Or should I just cut my losses and get a new computer/hard drive/whatever?
Also, before this happened, my computer reset itself for no reason when I didn't use it for a few days (ie my desktop was wiped clean and all my files had been moved to the C drive). I was able to recover everything; but seeing a blank desktop instead of my usual wallpaper when I turned it on gave me quite a scare!

Luckily, I backed up all my files just the other day, so I don't have to worry about losing all the artwork I just scanned (among other things) if I dump this computer for a new one. But I'd rather not spend money on a new computer if this problem is easily fixable.

Any help or advice would be much appreciated!