Before now, I was running all of my games with the integrated Intel HD 4000 graphics with success. My current games are not very graphically challenging at all; two most played are Team Fortress 2 and CS:GO. I've been running both at 720p and medium-low graphical detail and been able to play at 60+ FPS all the time.
A week ago (after many hours of research), I decided on the MSI Radeon HD 7850 to power my games in higher detail. After installing it in my case and plugging it into my PSU, I booted up Windows (64 bit) and installed all of the latest drivers from AMD's site for the 7800 series for Windows 7 64 bit. Opened up TF2 and put the resolution and most graphical settings to the max. After I was in a game, my FPS was steady (around 90) for a couple of seconds, and then I experienced massive fluctuation, with the FPS jumping from over 100 to 2 within seconds and continuing to bounce around everywhere in between, rendering the game completely unplayable. Disappointed, I tried a few other games with the same result. I made sure I had the most recent drivers (I did) and tried again. Unplayable FPS again. At the recommendation of a programmer friend, I disabled the Intel graphics via Device Manager and rebooted the computer. Same thing happened, game opening fine and everything until I'm in game, when the frame rate ranges from 2-100 and changes every millisecond. The device manager said that the HD 7850 was working perfectly, and my WEI jumped up considerably in the area of graphics.
I spent several hours troubleshooting on various forums, including this one. Haven't seen anyone with the same problem.
Other things I've tried:
-Checked to make sure the card itself was installed properly (it was)
-Uninstalling and reinstalling all of the Catalyst program and all of the AMD drivers
-Rolling back to the drivers the card shipped with (wouldn't even OPEN the games)
-Completely uninstalling Intel graphics and trying all of the aforementioned things again
All to no avail. At this point I decided I would RMA it and powered off my PC / removed all cables, removed it, and put it back in it's anti-static bag. Plugged everything back in, booted it up, and reinstalled the Intel graphics drivers for the HD 4000. Launched TF2 to find the same FPS jumping happening (even after I had turned the resolution / detail level down).