Hio
The screen flipping on and off is normal when windows first sees the other gpus. If it continues to lose the signal, then its probably the psu.
Run the AMD uninstall utility, then try the 12.11 beta drivers. They have run every gpu mix I've thrown at them.
http://sites.amd.com/us/game/downloads/Pages/downloads.aspxMy plan 'B' will be to create a virtual pc instance for the 7970.