Problem with SLI.

I have just installed a second video card in my system but every time I enable SLI my computer crashes. I have lots of cooling and my temperatures appear to be normal, but nothing I do seems to help fix this problem except switching it to single gpu rendering. I have reinstalled the latest drivers, and I have also updated my motherboard's drivers and the problem persists. I have even cleaned out all the dust from my system to cover all my bases. Any suggestions?
2 Evga Nvidia GeForce 6800XT 256mb PCI-E video cards
Pentium 4 3.0 ghz
2 gigs of RAM
500 W PSU
ECS C19-A SLI V 1.0A mobo (nforce chipset)

 

You might check your SLI connector block. Thats the communication block that ties the two cards together on the topside of each card. It is important that this block has uniform compression so that the tines in each connector make reliable contact. Make sure ( after unplugging computer from wall socket ) that each of your video cards is fully seated to the motherboard. Next, use screws in the backplate to hold each card in place. Then finally, install the SLI jumperboard compression fitting. This is a metal fixture that holds the SLI jumper board in a stable configuration providing for equal pressure applied to each connector end. It may look like a piece of unnecessary junk, but the manufacturers have their reasons for including it.

 

I can't seem to find this bracket it never came with my mobo. Where can I get one and would this be causing many of the problems? Even if it does seem to be fitted on rather well. I was also poking around my mobo guide and found out that I needed to connect a 4 pin power cable to the auxillary 4-pin power connector lableled ATX4P1 on the mobo. I connected the cable but still I have instablility with my system. Same crashes and lockups.

 

Anybody?

 

I tested my own mobo, with the compression bracket removed. It still works. It probably will work fine for several heating/cooling cycles. I noticed, your video cards have a power connector at the back edge. Hopefully, you've hooked these up as well. I've got a couple of overclocked 6800GS boards, and I had originally daisy-chained power from one board to the other. I had a few problems, and even after getting the latest drivers for mobo and cards, I still wasn't happy with the lockups and shutdowns. Then I got a clue while searching the net, that my power supply might not be providing enough power. Well, I've got an adequate supply so I eventually fed each card from an individual connector. Problem solved. I hope that helps.

 

I figured it out. The video card I just bought is busted. I switched that card to the primary display card and there were artifacts all over the screen at startup and the computer screen just went black. I'm shipping it back for a replacement now thanks for the help.