If when you are watching Live TV on Windows 7 Media Center and if every time you change certain channels the screen goes black, you may want to see if this fix helps you.
Windows Media Center Black screen
Open regedit and navigate to the following key:
On the right side, change the value of REG_DWORD, TimeholeThresholdMs to 3000 and see if it helps.
This value configures the largest allowable time difference between the audio and video streams, in milliseconds.
The default value is 2500. In some regions, certain broadcasts have been observed which contain a larger time difference.
Changing this value to 3000 may resolve the problem.
KB2430365 explains that this behavior occurs when the TV broadcast has a larger-than-expected timing difference between the audio and video signal.