You cant just crossfire any graphics cards together, they have to be from the same series. like 6670 + 6650, or 6670 + 6670, but not with 65XX. Just remove your 6550 and just use the 6670. Crossfiring low end cards gives is a bad idea anyway. You will get inconsistent performance, stuttering, fps drops etc. Crossfire only works well on high end cards where FPS can be kept high enough to eliminate the stuttering.