My Sharp TV only support 1080i, so I use a DVI-DVI cable to connect a monitor, then use Mini DisplayPort to HDMI adapter connect Sharp TV. Then boot Mac mini, I got Open Screen on Monitor, and I set HDMI adapter to 1080i, then I power off and unplug DVI cable and boot again. Well, I got what I want on Sharp TV, it is 1080i, but I found a 720p, I selected it, now the TV becomes to black screen with "Invalid video signal"! I reconnect monitor, so Sharp TV is ok, but if I unconnect monitor, the sharp TV will be black screen. I thought it might be some display settings are saved, because it was good when I first use TV after set to 1080i, but I selected 720p that is PAL TV, not for mine NTSC TV, after that selected, THe sharp TV can't be used alone, how can I reset display settings? what can I do for this case? Please help me, GOD!