Two related issues:

One - Alt - tab in game gives a black screen, alt - tab again puts me back in game

Two - Exiting game results in black screen -

Press Esc to get back to login screen
At login screen press Esc or click Exit, confrim comes up
Click Yes
Splash screen
Left click or Esc

Then get a Black screen

Windows is running can talk via Skype but cant see it

Work arround -
If I do Ctrl - alt - Del (stiil back screen) down arrow once (to switch user) rtn
takes me to windows login screen At that point screen reappears