problems with dolby digital surround sound on the rca rt2250 a/v receiver?

I have a RCA RT2250 audio/video receiver hooked up with my TV and i can not get the 5.1 Surround Sound to work. The only 3 audio settings i can select are Pro Logic, Stereo, and 3 Stereo. I have had this system for a whlie and it really bugs me that i cant get the SURROUND SOUND to work. I have many speakers throughout my house connected through a speaker selector but i do not think that is the issue because when i hit the Test button for the speakers they ALL produce noise (one at a time of course). So i need someone to please help me. thanks.

the manual can be found here for reference.

http://support.radioshack.com/support_audio/doc61/61791.pdf

The problem is not your receiver or your speakers , it's what you are trying to get from standard TV. You cannot get Dolby Digital surround sound from standard TV, it is broadcast in two channel or stereo sound only. HDTV is broadcast in Dolby Digital, so unless you have HDTV you cannot get Dolby Digital surround sound.
However if you switch from Dolby Digital to Dolby Pro-Logic 1 or 2, you should be able to hear some surround sound.