Computer not shutting down

[Siphric_Acid]

I just installed vista premium 64 bit yesterday and it shut down perfectly fine. Today however when I tried to shut it down my monitor went blank like it should but the computer kept running for 20 minutes before I decided to just hold the power button until it turned off. Is there something wrong with my computer or is windows trying to update like it does in XP when you power it down? Just put it together a few days ago and now wondering if I did something wrong if its now powering down.

Specs:
MoBo: Abit IP35 Pro
CPU: Q6600 G0
GPU: GT8800
PSU: Corsair 520HX
HDD: Western Digital Raptor 150g