Bravo is not part of Comcast's Basic package. You're most likely getting the unscrambled QAM version and will not get guide data until you get a cable card and the proper digital package.
You need to get one of their digital packages and a cable card. I think the Digital Starter package is the cheapest one that has Bravo.
S2, S3 (OTA), TiVo Hd, Premiere (OTA), Roamio Basic (Comcast Cable).