The only way to remove Windows Media Player 12 on Win7 is this:
1) Remove and the Install Windows Media Player thorugh Windows Features:
Click Start Menu -> Run [Or Win+R] -> Type "optionalfeatures" and press OK

More Info Here:
http://windows.microsoft.com/en-US/windows-vista/Turn-Windows-features-on-or-off
2) Or you could try reinstalling windows 7
More Info Here:
http://windows.microsoft.com/en-US/windows7/Installing-and-reinstalling-Windows-7