*Try running 1 card only (try each one in each slot)
*Try running with no GPU at all, use the IGP of the 2600.
*Try each ram stick in each slot individually.
*Make sure everything is updated.
Off topic: why did you buy that PSU???? you could have gotten dual GTX580s and a nice 850w PSU instead of that, and unless you're doing heavy video editing/decoding/encoding/transcoding/running VM/use fraps with high details there is no need for an i7.