I recently upgraded some debian installations to the currently newest Version (wheezy).
While most of the upgrades went very smooth, I ran into some trubles updating a system running on a Intel Atom Board.
As I reboted the mentiond system to boot the new kernel the VGA signal droped.
In the end it seems to be a bug in the
'gma500_gfx' module witch caused the Graphic-Blackout.
After blacklisting the mentiond modul, it worked again as it should.