Need more information ....
* brand/model TV?
* how is the Tivo connected to your TV (inputs/outputs, cables, connectors)?
* what is your video souce (cable, cable box, satellite receiver)?
* if you're using a cable box or satellite receiver, how is that connected to your Tivo?
* have you tried rebooting your Tivo (disconnect power, wait 30-sec, reconnect power)?
Sony SAT-T60 120GB (v3.5b)
HR20-700, HR20-100, HR21-200 HD DVR
HR10-250 HD DVR 400GB (v6.4a)
H21-200 HD Receiver
R10 DVR 160GB (v6.4a)