Now days Cable TV video is digital and encrypted. You need a special kind of tuner to receive Cable TV programming, one what supports CableCard.
Cable companies required to rent it to you, usually at low rate of $5-6/month,
However there very limited amount of such tuners available on the market.
Ceton InfiniTV 4 is one of them, however it's $400 plus cost plus issues and delays with shipping doesn't make it easy product to get...
Honestly besides Ceton, ATI used to make such tuner, but they dropped it