Airplayer running on windows XP does not consistently display video clips

The Airplayer is running Windows XP with the latest patches and etc.  The flv clips would be visible intermittently, there's no pattern to it.  The clip is being played as you can hear the audio but the screen just goes black.

Any ideas?  I thought that MP4 was the culprit so I convert the clips to flv but to avail.  I have other flv clips without audio and they works fine every time.

Please help.  Thanks.
Thomas

mmm I can only think it's related to the hardware used.
What are the specs? When running on our mediaBOX 2.6GHz Dual Core, FLVs play very nicely, even at HD H.264