FC16 screen continuously cycling, blacked-out, only visible for short time every few seconds.

[Ron Flory]

  Since a recent 'yum update', my FC16 display is blacked-out, only
flashing with visible content for a very small fraction of a second
every 2.5 seconds or so.  Needles to say, this make it very difficult
to use- luckily I still have remote access...

  I have created a bugzilla entry:
      https://bugzilla.redhat.com/show_bug.cgi?id=828454

  Graphics card:
     "nVidia Corporation G94 [GeForce 9600 GT] (rev a1)"

  The screen begins cycling its black-out upon startup at the initial
switch to graphics mode. This continues during the Fedora boot-progress
logo and never clears.

  I do use Xfce (no desktop wars, please), but don't think this is a
factor because the black-out begins so very early.

  Has anybody else seen anything quite like this?

ron