"One of the biggest problems that I’ve run into with HDMI connections is one I fondly call the “black screen of amnesia.” This occurs when you power up a device and the TV doesn’t recognize it. Sometimes, flipping to a different input on the TV and then back to HDMI is enough to jog the connection into working again. But I’ve occasionally had to power everything down and restart in the right sequence to get things working."
I had this a couple of times, and IIRC my setup was "TV" not "flat pannel". Changed it now.