I was having the same issues on windows 7 64 bit, and found a solution. If you hold down shift while pressing play on the larian launcher with the game set to dx11, and have the bg3dx11.exe set to run as administrator, then the game will launch fine. Someone in another thread that I can't find right now found out that windows 7 had 2 versions of run as administrator, one which requires shift to be held in order to actually elevate priveledges.
