Hi,
1. Does the issue occur with other files as well?
2. Does the issue occur only when you stream videos?
3. From where are you trying to stream videos?
4. Does the issue occur with a particular URL?
5. Are you watching live video or recorded video?
For now you may try the steps provided in the following article and check if that fixes the issue.
Open the Windows Media Player Settings troubleshooter.
http://windows.microsoft.com/en-US/windows7/Open-the-Windows-Media-Player-Settings-troubleshooter
Reply us with more information so that we can assist you better.
Thank you.