I had the same problem with GTA V and got it working last night, you have to launch GTA V in "Direct X 10" Im using Steam to launch mine and with that all you have to do is right click on GTA in your library go to properties, and then launch options. From there in the command line put -DX10 to force launch it in Direct X 10 mode and you should be all set. For any other games that do play and then crash with a reboot with the Wattman message you have to lower your max clock settings in wattman down to 1800mhz or so to stop getting that crash, I know it sucks dropping them down some but it really does not impact the game because it hardly maxed out anyway. I can get everything to run but when i play Fortnight it seems to cause it to crash after a few mins unless i drop the max GPU clock down to around 1800mhz, same thing with GTA V but not as bad just takes some playing around with till you find the sweet spot. Im using the 50th Anniversary Card and that seems to do the trick for me, maeby the GPU clock is to high outta the box for this thing to be stable, But anyway thry the -DX10 for GTA on steam or find out what you need to launch it in DirectX 10 if your on a diff platform than steam. Hope this helps, its been a ruff few weeks of problem solving. AND ALWAYS make sure you REINSTALL YOUR AMD CHIP SET DRIVERS!!! after you use DDU to remove old video drivers or you will have problems launching games that already worked before removed with DDU
