Q: K9A2 Platinum 790 FX 4gb of crosshair ram AMD phenom X4 9850 HIS ICE Q3 3870 and visiontrek 3870 OC edition in crossfire 600 watt PSU from thermaltake
A: Generally you try to match the two videocards as closely as possible. Same manufacturer, same type, and same speed. Those two cards aren't matched except for the GPU. You may be able to get them to work together, but you'll probably have to downclock the cards to stock speeds to facilitate card - card communication. Once that's done, you have a much better chance.