Windows Media Player exits full screen while watching movies

Problem:-

I am using WMP 12 and while watching movies the full screen exits after 15 minutes.How to fix?

Why it’s happening?

Generally it happens if screensaver is enabled during playback.

Resolution:-

1] Open  Windows Media Player

2] Press “Alt” >  “Tools” >  “Options”

3]  Under the Player tab locate “Allow screensaver during playback” option and if it’s checked then uncheck the box against it.

4] Click OK.

Other suggestive measures :-

How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7

http://support.microsoft.com/kb/929135

If the issue persists, I also suggest you create a new user account to test the issue.

Fix a corrupted user profile
http://windows.microsoft.com/en-US/windows-vista/Fix-a-corrupted-user-profile