Sorry, but I cannot help much with such cryptic answers. There's a big difference between watching CNN HD and a movie like Jurassic Park in DD 5.1. In order to get troubleshooting help, you need to start by playing a program that should have plenty of bass. Then, we can use that to figure out what's happening with your source and/or receiver.
Also, what receiver do you have?
How do you receive TV signals?
How is your TV source connected to the receiver?
What are the audio output settings of the TV source device?
When you feed the TV signal into your receiver, what format(s) does the AVR report it is getting?
Are you using any surround modes in the AVR to modify the TV signal?