Vista Home Premium x64 won't install

Hi all.

Sorry if this topic has been covered before, I did search first but
it's late and I may have missed it. I have just built a new system and
bought Vista Home Premium x64. I have tried to install it twice but both
times it locked and then turned off the pc just after the Please Wait,
running Vista for the 1st time screen. The first time it locked on the
background selection screen. The mouse and keyboard both stopped working
then the machine powered down about 30 seconds later. The 2nd time it
happened a few screens earlier.
My set up is:-

Quad Core Q6600
Asus P5N32-SLI Premium Wifi AP Edition
2gig Corsair memory
Geforce 8400GS (Bought it as a stop gap because the 8800GT is out of
stock and I wanted to get the system up and running.)
Logitech G15 Keyboard
Logitech G7 Mouse
SATA 80gig HDD

Does Vista make any requirements with regards to graphics card? I can't
find anything on the net but thats the only thing I can think of.

Any help would be greatly appreciated.


--
Gnorman