Some avi's my son took with his fuji camera at vacation bible school will not play in windows media but the one taken with the vivitar did.

More precisely it appears to be playing but only a black screen appears in windows media player.

If I import them to windows movie maker they play in the movie maker window and I can covert them to wmv's so they now play in windows media.

Why? What codec am I missing? When they come off the camera they have the .avi extension. This is the same camera that the fireworks video was taken and as it came off the camera it did play in my media player so I am baffled. I have made no changes to any of my settings on the computer. Is it possible he set something wrong on the camera?