please, note that Microsoft has very strange way to work with channel lists in Windows 7 Media Center - they use some predefined channel lists based on the location you chose and area code you put during the configuration wizard and it's very common to get "no tv signal", because Microsoft just use wrong parameters in the channel lists.
while with DVB-S/S2 is possible to solve such troubles with playing around like you did it's much worse for example for DVB-C as you can read here:
http://social.answers.microsoft.com/For ... a5ddb2fbc4
and
http://social.technet.microsoft.com/For ... febc35b888