Sorry, I was sleepy when posting earlier and forgot to mention specs:
Windows 7 64bit and two Radeon 4850s in Crossfire mode. No overclocking. Rig is in good condition, and fully up to date.
Edit: (seems I still haven't woken up!) I'm running dual screen but switching to single didn't help either. I just don't wanna hear I need to disable crossfire 
Edit - The Sequel: Disabling crossfire = no help