Second monitor on iMac not working with Lion I have a mid-2011 Thunderbolt 21.5" iMac. A secondary monitor is connected to the iMac with a Mini DisplayPort-to-HDMI cable (a single cable, not an adaptor and cable).

When I was running Snow Leopard, the monitor worked just fine. After upgrading to Lion, the second monitor just has a black screen, and quickly goes into power save mode.

I have already tried resetting the NVRAM (as described here: http://support.apple.com/kb/HT1379) and resetting the SMC (as described here: http://support.apple.com/kb/HT3964).

Has anyone seen this problem? Any other suggestions for solutions?
As it turns out, it was the Mini DisplayPort-to-HDMI cable. I connected the secondary monitor with a Mini DisplayPort-to-HDMI Adapter and everything works fine.

To the best of my knowledge, the cable is fine, although, apparently, it is an unlicensed HDMI cable, and manufacturers can no longer sell them. Has Apple dropped support for these? Not sure. At least everything works again.