Windows Vista Media Center live tv sound but no video

I know, I know, you probably already did this, but double-check all the physical connections. Is the antenna or cable coming into your TV tuner card securely plugged in? Is the tuner card itself seated properly in its slot inside your computer? Sometimes a slightly loose connection is all it takes to mess things up. It's like making sure the speaker is plugged in before you expect to hear sound!

Media Center Software Glitches - The media center application itself might have a temporary bug or configuration issue.

If you're using an antenna, is the signal strong enough? Try repositioning the antenna or consider using a signal strength meter if you have one. Weak signals can lead to audio but no video.