I also had some strange issues with my multiple monitors until I changed which monitor was attached to each connection on my video cards. I was also using an adapter which caused major problems.
I would suggest trouble-shooting by process of elimination.
1. Go to this website to make sure your not missing anything on which should be your primary monitor and secondary displays:
http://www.geforce.com/hardware/technology/surround/system-requirements2. To rule out software - do what Haldi says and remove the current/previous driver using Display Driver Uninstaller DDU, reboot then install the latest driver version.
3. Have you tried to use 2 monitors in surround? I would suggest using one monitor connected via HDMI and monitor two connected via DVI. If this works correctly then it may be an issue with the adapter (display port to DVI).
Good luck to you. I feel your pain.
-b0n3z