Had a similar prob, a laptop would not turn on HDMI port, etc. After a while developed a little black magic dance of opening display properties, change settings, click heels three times, detect displays, squirt of holy water, close settings, change resolution, hum first movement of HMS Pinafore, apply settings, turn around anti-clockwise, reopen settings, etc.
It used to work it out eventually, but certainly not plug'n'play. You have to basically trick it into rescanning the HDMI port. And every machine seems to have a different level of HDMI petulance, it seems.