Ubuntu 12.04 freezes on login screen

This problem was present in 11.10 version and remains after the upgrade to 12.04 LTS.
Ubuntu freezes on login screen which makes me suspect a video driver. This computer is Acer Aspire On 722 (12" netbook).
What I have noticed is that if I boot to Windows 7 first and restart - Ubuntu will load without freezing.
It is almost as if the video card establishes a mode from Windows 7 and then Ubuntu 12.04 works on subsequent restart.

Can you offer suggestions on what to do next?

Thanks in advance,
                                      Milan