Vista wont shut down

I have been having problems with shutting down windows vista when i

hit the shut down button vista closes all the programs and right when

you think its going to shut down and then i get an error sound and

nothing happens it just shows my desktop and when i move my mouse to

the middle of the screen it shows that little circle thing spinning

and my computer never did this i just built this computer a few months

ago and i had some problems with the HDD's and raid 0 but i never did

it. It was to messed up anyways after i got the computer running it

was working fine until about a week or so ago i also noticed after the

last update some things havent been working right and that update was

an important one to the ones that automatically shut your computer

off. Well ok this is enough writing for now lol. Oh and here are my

specs

Motherboard: Asus m2r32 ati chipset

Video card: 2900 XT HD from ATI (ATI's version of the 8800)

CPU: AMD 64 X2 5400 2.8 GHZ (dual core)

Ram: 4Gb of corsair dominator

Power Supply: 650 watts (don't remember brand)

OS:Windows Vista Ultimate x64