apparent repeated Samsung C series HDMI failure

I'm hoping someone can shed some light on an unusual HDMI problem. I've had the HDMI input fail on my Samsung LN46C750; the set is 6 months old and was set up with my Denon AVR HDMI output feeding the Samsung HDMI 1 input. All was well for months until I powered up the set one day and received a "no signal" message. I tested by connecting my components (the AVR, Dishnetwork RXer, and Roku) directly to the Samsung HDMI inputs and still received the "no signal" message for all three connections. I tried a factory reset on the Samsung, then tested all three components again with three different cables, same results. I ultimately opened a service request with Samsung and had the main board in the set replaced. I fired everything up while the service person was here with my AVR connected to the Samsung HDMI 1 input and all was well. The next day, I received the "no signal" message again.
I haven't contacted Samsung yet; I don't mind having another service call for a main board replacement, but it seems odd that two would fail.
I tested again by connecting three different components directly to the Samsung with three different cables. When a device is connected to, say, HDMI input 2, then that input will appear in the source list like it's a valid source, but when selected does not work and I receive the "no signal" message. When no cable is connected to a particular HDMI port, that source is "greyed out", and a "check cable" message is displayed.
Can anyone offer any insight into what's happening? Am I really just unlucky and have another bad main board or is there some weird HDCP/handshake thing going on with my AVR and other components? One more thing to mention is that I had the same AVR and gear connected to a very similar LN46C650 for over a year without issues before I switched to the C750.

I've tried the AVR, Roku, and Dishnetwork receiver individually using three seperate cables. I've tried all three individually on multiple HDMI ports, and I've tried them together on inputs 1, 2, and 3.

walford-
all devices are on a surge protector and/or UPS w/protection. I'm starting to believe there's some bizzare HDCP thing/hanshake or sequence of events creating this problem.
This morning, I fired up the LN46C750 with my satellite receiver connected to HDMI 1, and received the "no signal" message. Then I took down my 22" B series Samsung from the kitchen and fed the satellite receiver to its HDMI input and all worked as expected. I tried the AVR's output on the 22" as well and all worked as expected. When I reconnected the AVR to the LN46C750 HDMI input 1, it came right up as though nothing had ever happened.
What the hell is going on? This is incredibly infuriating, never knowing if the damn thing will work and having to rearrange all my connections using component cables every time it fails.