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!
I hope these help!
Windows Outreach Team
Looking for a little help. I have Windows Vista and I am finally trying to use the Windows Media Center to record live tv. I live in an apartment building where the landlord includes Charter Digital Cable. We don't have a tuner box, but instead just plug our TV straight to the coaxial jack in the wall.
I tried plugging a coaxial cable from the TV tuner on the back of my computer straight into the wall. When I run the setup for Windows Media Center it says it can't detect a TV signal.
Any solutions on how I can get full cable tv through my Windows Media Center?
The way it looks I could buy a digital antenna and connect that to the back of the computer, but then I'd be limited to the digital network channels (ABC, NBC, etc) and not full cable.