Just performed dxdiag and attached it to this post.
How long did you stay on Windows after ALT-TABing the game? For me the crash usually occurs after a few minutes but once it took half an hour to occur. Maybe you didn't wait long enough?
To describe the issue again, ALT-TAB does work fine but while on Windows (with the game reduced after ALT-TAB), the game eventually crashes with a Windows blue screen showing for a second followed by a return to Windows with the following fatal error message:
Again, this issue started out of the blue from around season 3 without me changing anything on my machine. I tried reinstalling the game, reinstalling Windows. The problem persists across game updates, across NVidia driver updates. And I'm not the only user reporting this issue. So it is VERY UNLIKELY to be caused by a software or hardware issue on my machine.
