Does the problem affect ALL videos? Or only some of them?
If you try using another player, does those videos play correctly, or do they show the same problem?
If the problem also affect the same videos, in the same way, when using another player, it looks like the file have some missing parts.
If it affect ALL videos in the same way, but they play correctly when using some other player, you should think about switching to some other, more serious, media player. There are several very good FREE ones available from all over the web. A simple Google search for "media player" will return a large choice.
Some good choices: VLC and Winamp. Both can play more formats than windows media player.
Electro, June 2011