blank screen on game load

after clicking the play button on the launcher, the screen goes blank except the taskbar shows through (appears squashed horizontally) and I can see and move the mouse cursor, sound plays and apart from not being able to see .. appears to be running ok

.. tabbing in and out the screen goes completely blank (except for a mouse cursor)

laptop - alienware m11xr2 - NVIDIA GeForce GT 335M with Optimus Technology
(72 CUDA Cores, 450/1080/1580 Core/Shader/RAM) and Intel HD Graphics

latest directx and nvidia drivers, optimus configured all applications default to NVIDIA card. also added specific rules to nvidia driver config to ensure diablo iii.exe and diablo iii beta launcher.exe use nvidia card

edit: clarified