First steps should be to make sure your up to date with Windows 7 updates all the way through.
Second is to make sure your mother board is up to date.
You should be on mother board BIOS M3A78-CM BIOS 2801
most recent. Get a USB flash drive down load your BIOS to the USB flash drive. Go to your BIOS and make sure your first boot is to USB. This will flash your mother board to the most current BIOS. After, go back to your BIOS and boot up sequence back to HDD drive again or default anyway.
Let's retry your old GPU and see if it works over the 6950. Your GPU should be up to date with GTX 260 drivers
. If it works then it's your new 6950 that is bad.
If it still gives you a problem you can go back to Catalyst Software Suite 11.9
most recent AMD driver and put back the AMD 6950.
Let's do some trouble shooting. Easiest to hardest.
Humor me on this one...first try this little monitor test....unplug your power cord to your monitor and DVI/HDMI cable. Wait 10 mins at least. Replug and see if it works.
Now if that doesn't do anything and you reboot to wallpaper alone. Bring all clocks back to default on everything. No over clocking.
Try to reboot and see if default clocks change anything. IF it dosen't for next test leave it all at default.
This next process is a killer and takes some time. Test the RAM first by inserting one RAM at a time and then booting up. First try DIMM A1 slot 1 if your counting from CPU to right. You should be able to boot up with both.
IF it does then try one RAM at a time again but in DIMM A2 which is slot 3 if your counting slots from CPU side to right. Again you should be able to boot up with each one.
This test will verify that your RAM and RAM slots are working and fine.
Trial and error when trying to diagnose these kinds of problems.
This will knock out some of your possible issues you need to make sure isn't a problem. Let us know if any of this helped.
WOW just noticed your my 2,000 post.