Upgrade to 12.04 does not boot

I have upgraded to 12.04 via upgrade mamager.

I cannot get the image to boot (blank screen) after the grub menu.
grub seems OK.
I can get the previous unix version to run in recovery mode (rahter shaky).

Booting 12.04 in recovery mode displayes very early the message
firewire_ohci: Failed to set link Power Status

There is no firewire installed on this acer travelmate 8210 to my knowledge....

Is it possible to disable firewire for booting?

Is it possible to downgrade again to the previosu version of Ubuntu?

Any help appreciated!