I have a new Samsung PN50B450B1D. I've hooked up my Toshiba SD-V392SUA DVD Video Player & Video Cassette Recorder from its DVD component out and DVD audio (L/R) out jacks (switching the S-Video/Component video selector switch to Component) to the Samsung's component in 1 jacks. I powered on both the Toshiba and the Samsung and started a DVD playing. Then I pressed "Source" on the remote and tried to select AV1 but it responded that it was not connected (AV1, AV2, Component1, Component2, HDMI2/DVI, and HDMI3 were not highlighted and at the bottom of the list, which the setup guide says means that the device(s) are not connected, I tried AV1 anyway--I also tried all the other external devices just to make sure).
Although the cable set I was using was new, I swapped it out for some others I had and went through the above again with the same results. I also tried connecting to AV2, but, of course, that didn't change anything. I don't know what else to try.