oblivion wont run

Hi i am having trouble running oblivion on a pc running vista home premium. It installs ok but wont run? Any ideas?
Mactronix

Thanks for the reply im not sure if it could be the graphics as i can get to the screen that detects the graphics and it sets itself automatically to match the hardware.
On the other hand it is running onboard graphics so i will try and give you a list but it wont be precise as i will have to do it from memory as it isnt my pc.

e4300 dualcore
1 gig ram
G965 on board graphics basically an updated x3000 core to run aero(i know this as i had to check for the owner as he thought he got stiffed on the upgrade).
Not sure on mobo but the pc came from dell!(yea i know)

Hm i just had a thought i remember reading some where that oblivion uses 400meg of ram and im wondering how much vista uses if its a lot and the figure for oblivions usage is right then it could be lack of ram?
Thanks again Mactronix