ASUS EN8400 GC - PC freeze and boot problems

Hi everyone - I'm having great problems trying to install a graphics card in my PC. OS is Windows XP SP2, motherboard ASUS P5VD2-VM, Intel Dual Core CPU, 1.0 GB RAM, BIOS Phoenix-Award BIOS v6.00PG. PC was built up for me from components, it is not branded.

Firstly - this works ok with the on board video card, but that is very poor quality/slow and is not sufficient for many applications.

I originally tried a couple of ATI Sapphire cards (e.g. X1650) but had problems with a known issue which is the ATIDVAG2.DLL file endless loop - this is a known issue to which there appears to be no viable solution (?).

So I bought a ASUS EN8400 GS on the basis that this uses a different driver; however I am now experiencing problems of a different kind, namely (1) pc does not always boot up correctly, it beeps then tries to re-boot repeatedly; eventually it fires up and (2) when it eventually all boots up, after a while the PC freezes, and the only way out is to power off. ASUS support says return the card to the dealer!

There are no error messages, nothing. Hardware monitor says all is working correctly.

Any ideas out there?

Thanx - Andy