I just purchased a new Home Theater from Best Buy.
Reciever: Sony STR-DG710 TV: Magnavox 42MF231D (42" Plasma)
I can hear all of my inputs: cable, Xbox360, and tuner. But I'm not getting a picture at all. I have the Xbox and Cable both connected to the Sony with Component. The output to the TV is HDMI. I don't understand what else I could do invoke a picture on my TV.
Your receiver is not "upconverting" from component to HDMI. For HDMI out to work you will need to use the HDMI inputs from your various devices. Since this is not possible from your X Box, the best solution will probably be simply using component switching and you can use the HDMI from your cable box to your TV, use one of the digital outputs from your cable box to your receiver. You will then have to switch inputs on your TV but it will be much better than the black screen!