I don't know does the 6870 use two 6pin conecters? When you hooked up to the integrated graphics did you still have your 6870 in its slot? Because if you did that is why your integrated GPU did not work.
Also could you post all of your spec's and what is the brand of your PSU? Also what happened to your first card when you had to RMA it? Need the story on that as well. Get back to us please.
The 6870 needs two 6 pin connectors to be powered properly. The 6+2 pin will work with the card, just detach the 2 pin from the 6 pin for the second connector.
Now when you say it freezes Windows, how far into the boot do you get? Does it freeze at the starting windows screen, or do you get to the desktop? Try booting into safe mode and install your drivers from there. You can get to safe mode by hitting the F8 key before you see the starting windows screen.
Try shutting down and removing the plug from the wall and the cmos battery from the motherboard. Also remove the video card from the slot and then try to boot up your computer after you plug everything back in except the video card and see if you can get the intergrated graphics to work.
Thanks everyone, I found out what the problem was. For some reason there seems to be a compatibility issue between my card and the mobo. When I tested it on the other PCIe slot, it worked out just fine with no issues. I don't know why this is, but I'll run some diagnostic tests until I figure out why this happened. Once again, thanks for your contribution.
Whoops. Sorry I forgot to reply. I have two PCIe x16 slots, both are working fine. I ran a diagnostic and confirmed that some of my Intel motherboard features were conflicting with my AMD drivers. I disabled it in my BIOS and that fixed the problem entirely.
My only concern now is that the card isn't performing quite as well as I expected. Maybe I'm a fool to think that nVidia sponsored titles would run much better on newer AMD hardware, but still, it's somewhat underwhelming.