Regarding the "won't shut down", have you tried holding in the power button on the case for about four or five seconds? That usually does the trick for me, and at least I can then switch off at the mains. I know this trick probably puts the computer into "sleep mode" - 'cos sometimes when returning the mouse to it's housing, the flipping thing restarts. lol
I think I've read threads of others having similar problems with XP - try the search facility.