We've seen the HDTV HDMI ports get "confused." I won't go into any technical discussion about HDMI's bag of hurt here but try the following.
Remove all cables from the HDTV along with the POWER. Go make some tea and then apply power and try it again. I've lost count how many times a cup of tea has cured this one. If not, you make more tea to call for service.
I am having a issue connecting my Mac Mini (2008 edition) to my sony Bravia 55HX750. I am running OS X v10.6.8.
The video shows just fine on my old TV through HDMI but when i move it to to the bravia it will not give a signal supported even though i have it set to 1080i.
I had the Mac hooked up earlier to the Bravia and when i was messing with the video settings on the Mac it stopped working when i set it to 480p.
I have reset the VRAM/PRAM, run in safe mode, reset PMU, and reset the TV. Any help would be greatly appreciated.