There is an outside chance you are OK.
(1) I have had situations before where I thought for sure the TV was dead and powering off and on did not fix it. Sometimes it is really dead and sometimes it can magically come back to life if you disconnect the power cable (yes pull the plug) leave it for 30-45 seconds and then plug it back in again. I assume in these cases that the firmware got into a bad state and a hard reset of the power fixed it.
(2) Your other chance is that the problem only exists with the particular input you are using. I would try a differen HDMI input into the back of the TV or failing that I would see any of the other connection types (component, s-video, etc) supported by your cable box are working. If the TV comes on and shows a picture it may not be optimal but you are not dead in the water while you play footsie with the warranty folks.
Beyond that I got nothing except that it seems to me that Sony Bravia was endorsed unreservedly by a certain poster on here and I would seek recourse from him for bad advice. Even if you don't end up getting cash you can vent your frustrations to some degree.