The average user gets irritated when something doesn't work, and to make him really angry you only have to tell him to have a look at his own equipment. Still, sometimes there seems to be no other way. This rendering problem is such a case.
When your end user (or you) sees this:
the first thing he should do is: go to:
If he doesn't see a spinning cube, there's probably something wrong with his video hardware. My personal experience: Updated my video driver, didn't help, switched on hardware accelaration, everything worked.
Hope this helps.