Some graphics-related aspect of the computer just failed again.  It was only running Windows 7 following the last service.  It took a bit longer but the symptoms are essentially a gradual version of the same issue.  The screen would flicker off every day or two.  Now it does it pretty soon after I'm able to login to Windows.  The odds are now probably in favor of a product defect rather than a software-hardware issue.

Ironically I'm three days out of warranty... but I first noticed the problem last week.