As the title. though all ok when i play with one 4870x2( anyone of two cards), but when i set both two 4870x2 cards to make CrossfireX, the system can't post at all. there's no vga signal output. but the debug led of mainboard shows system boot ok till now i have tried : 1:adjust the jumper of the back of 4870x2 2:change another one crossfire bridge cable but doesn't help. i have tested both two pci-e slot with single 4870x2 card, works fine. but still no post when crossfireX. OMG..... my components: cpu: qx9650 boxed mb: asus rampage extreme x48 vga: powercolor hd4870x2 x 2 power: tt toughpower 1500w ram: G.Skill F3-12800CL7D-4GBPI(2gx2) it that a compatibility issue? what should i do now ?