Hi I am in need of serious help, and I am not knowledgeable enough about computers to figure this problem out. First let me tell you my system specs: Phenom II X4 940,BIOSTAR TA790GX A2+ AM2+ HDMI MB, 2 HD 5870's, a brand new SSD with a fresh install of Win 7 Pro, a Kingwin 680w power supply, 4gb ddr2 800 ram, and a xigmatek dark knight cooler. All drivers are up to date as is Win 7. When I enable crossfire within 5 minutes of gameplay the system restarts out of the blue. Of the 2 hd 5870's one is an xfx that I bought a year and a half ago and the other is one I bought off ebay a few days ago that appears to be a reference card or HIS, but the card was brand new(made Nov. 2011 infact.) Not only does the system restart but it appears one of the cards fan turns all the way up while the other card feels like the fan isn't even on. Is it a heat issue? I try to manage both cards fans using afterburner but still same problem occurs. I have tried several 5870 configurations to ensure my new graphics card is good. Each cards works perfectly when installed alone and even in different pci-e slots.
My thoughts are these: 1. It is possibly a problem with the power supply, and when the system utilizes both cards it can't handle it. However, why would it appear that one card's fan is blasting while the other's isn't even on.
2. Perhaps the Mobo is faulty or the crossfire bridge I am using is faulty. Maybe I need to update my BIOS, which I've never done. I'm not quite sure but the selection of Mobos on newegg with crossfire is pretty weak.
3. And my final guess the xfx card simply won't work in crossfire with a different brand of card. I hope to god this isn't the problem because then I have a very expensive paper weight or I sell one of the cards used on ebay and lose money.
Any advice and suggestions are much appreciated. Thanks in advance. Also I am more than happy to upgrade the power supply and buy a new mobo, but if that doesn't work then I burned even more money and I'll feel sick.