I've recently upgraded my sons computer to sli using a second Evga 7800 gt vga cards. I removed it from Daughters computer and gave her a weaker card, she isn't gaming . My son was playing Oblivion and his vga card was just too weak. Now after adding the second card the game locks up and he has to restart the machine.It did not lockup before ,just crappy game play. All setting are at low,I'm sure that this psu can handle sli with these cards, but I don't know for sure . Specs are DFI lanparty SLI M/B, 1 gig of corsair xms ram and the two Evga
7800gt vga cards, XP pro os .

Tried the cards individually to see if one was a bum in 3D mode/load? Of course someone always has to mention the obvious...you plugged in any power connectors on the card, right? Also check the mobo. It might have an auxiliary power connector that's required when multiple graphics cards are installed somewhere. Might be in the form of a molex connector(usually tucked between the CPU socket and PCI-E ports).

I seem to remember the DFI motherboard as a 4 pin molex and floppy disk drive type connector for auxillary power. Are these both connected?

if the cards have different default clock speeds, swap the positions of them as the 2nd card gets the speed of the 1st card...

flashing the cards to the same firmware is a good idea and what I did with my 7800GTs on DFI NF4

The connectors are all connected. I have not tried the other card on it own in this computer. I just don't think that's the problem. And it is both the molex and the floppy dr. connector.

They should be the same, When I first perched them it was is I could go sli using them,which I did. They worked fine.

Also I meant to ask, Should I not be able to choose some sort of sli option in the bios ? I have moved over the jumpers( pain in the a**) and it shows sli in as being chosen in the Nvidia control panel.