OK, basically the HDMI on my 360 doesn't seem to work with my TV any more. No sound or video. I've tried 2 different HDMI cables and neither make a difference, my TV says either "Not Support" or "No Signal".
I've tried the hold Y and LT to reset the display settings, the console restarts, but still no signal.
I've also tried blindly adjusting the display settings, but with no luck (kinda hard to do if you can't see or hear anything.)
The problem started the day after I added a 60GB HDD, but that could just be a coincidence. I had used a Seagate 500GB USB HDD prior to that. I've troubleshooted with both HDDs connected, just one connected and with none connected, but still no luck.
However, I've tried my 360 on a friend's TV and it works fine. His 360 also happens to work fine on my TV with no problems.
My TV is a Kenmark 19" HDTV 50/60Hz 1080P. It doesn't have YPbPr connectivity.
My 360 is pre-owned from Cex, presumably a Pro. Wasn't supplied with a HDD so it's hard to tell.