Sapphire Radeon 4870 x2

Hi,

Just bought a pc over the weekend:
Intel P45 Skyberg Mobo
E7400 Core Duo 2.8 Ghz
2x 2GB DDR 3 Ram
Sapphire Radeon 4870 x2 2GB
320 gig Sata HHD
730 Watt power supply

I'm running Windows XP 64 bit and when I run games in full graphics the pc resets (it turns off and then back on) either just after I change it in the game menus or just as it starts to load. I’ve tried it in a few games – same problem. The games seem to run ok in low or normal graphics but as soon as I increase the resolution or anything the pc resets. I’ve taken it back for people I bought it from to sort out. I can think of a few reasons why it is doing this:
Faulty power supply, incompatibility with mobo or CPU, BIOS needs an update or there is an issue with windows xp 64 bit. I know it’s not a faulty card as the company I bought it from tested another 48070 x2 card in my pc and it gave the same problem. I downloaded the latest windows 64 bit catalyst drivers – didn’t help. I also messed around in the catalyst control panel.

HELP ME PLZ

I have no idea, the pc is back with the shop I got it from. Do you think they would be rookie enough to not realise that the amps are wrong or that the PSU is set up incorrectly? I think it's a Raidmax PSU - that's what I can gatehr from the invoice.

Turns out it was the power supply. I've now got a Huntkey 650 Watt PSU and it seems to be working fine Thanks for the help, much appreciated.

What is the normal runnning temperature of the card? It seems to be around 71 degrees in Windows. This ok?