I have tried to install different drivers for the cards, and I have tried installing a previous version that supports both cards. Neither worked. It seems to be the combination of the new card and anything but the new driver that makes GUIMiner not start.
Now, when I am running only the new card, Phoenix and Stratum Proxy, it stopped working tonight, a few hours after I started it. I restarted the miner this morning and it worked again. I hope it's a one time occurance, but I doubt it. It didn't happen with Phoenix and BCPool. Any guesses?
My estimsted rewards seem to be about right. I'm not exactly sure what they should be, but they are not in the 7 satoshi order of magnitude... Currently it's 0.00051612 and I've been running 200 MHash/s for 1.5 hours.
Maybe you should use next workaround. Remove one card from a computer. Run cgminer and if it works you will get kernel for that card. If it doesn't work change SDK and run again. If hashrate is too low use diffident SDK/driver and remove .bin file from cgminer folder. When you find the best combination backup .bin file just in case. Now remove the card and put in other card. Do the same but don't delete first card .bin file only second card .bin file if you don't like hashrate. Now put both cards in and run cgminer. It might work.
And just in case. When running windows you need to plug monitor or null plug into card. Did you?