11.04 beta Unity

I started Ubuntu with 9.04. Upgraded from 10.10 to 11.04beta around 2 weeks ago. Everything worked fine. Didn't like Unity at first but have got used to it and now prefer it. Last weekend I updated and got a message along the lines of "You do not seem to have the hardware to run Unity - use classic". Since then I have had nothing but problems - even with classic. During power on I get vertical white blocks appearing on screen for about 1/2 second. System seems to work OK in classic but freezes during shut down - have to hold reset button down to force shutdown. About once every 10 startups (not consistent) things seem OK and shuts down OK but then reverts to faulty mode. Reloaded completely 2 days ago with fresh 11.04 livecd and seemed OK (Unity worked again) but then reverted at next power up to " You do not seem to have ...." and problem is back. The real pain is the freezing during shut-down - quite intolerable.
Sony VAIO laptop VGN-A617S Graphics ATI MOBILITY RADEON X700.
Can't understand why sometimes Unity works and then other times apparently hardware is not valid.
Prior to the update last weekend it worked fine every time - including Unity.
Any clues would be useful. Really don't want to back to the Gates empire!