As far as I know, your video cards shouldn't be crossfired together. But I don't think that would crash your GUIMiner..
I disabled crossfire, no difference.
Also I forgot to say before, but when I had uninstalled all my drivers and restarted I was able to open up GUIminer and (I believe) mine correctly using my CPU. It went at about 2Mh/s as opposed to the ~350 with the GPU it was running at before, not that it was actually giving me any valid shares though.