:^/ I had similar trouble with mine. The demo had no troubles with Iron Man, so I bought the full version. Well, while Iron Man and other titles play with no trouble, some discs never showed any video, though the audio would play. Other discs still would play some parts well, and not others. For example, some would have no video for the menus, but if I navigated past them blindly the movie would play just fine.
Well, it turned out to be the codec used for compression. Mpeg-2 would not show video, while Mpeg-4 and VC1 would work perfectly. The solution was to reduce the screen resolution and color depth. Then Mpeg-2 would work.
;^) So now I just remember to do that whenever using my laptop to share blu-rays on my buddy's standard television.
If you're getting some movies to play well, but others not at all, you might want to try that, too.