Here are a few sites that can help you through the process of setting up your TV to Windows Media Center. They have some good information in them that I think will be able to help you solve your problem!

http://windows.microsoft.com/en-us/windows-vista/Troubleshoot-problems-with-watching-TV-on-your-computer

http://www.ehow.com/how_5865637_configure-media-center-tv-tuner.html

http://maximumpcguides.com/windows-vista/set-up-your-tv-signal-in-windows-media-center/

http://www.howtogeek.com/howto/9166/learning-windows-7-setup-live-tv-in-windows-media-center/

I hope these help!

Brett M,
Windows Outreach Team