HD 5870 HMDI problems.

OK, I have a fairly system. Asus sabertooth X58, HD 5870, i7 930, 12 gb mem, etc. Problem is, the gpu hdmi out isn't working. When ever i plug it into my TV, 40" Vizio, my TV just says NOT SUPPORT, but my computer realizes that they're connected. The reason I know this is due to the screen resolution menu. I have updated drivers for gpu but to no avail. i need help please help me.