I have an AOC i2353Ph which I use as a 2nd monitor with a iMac. Its connected with using HDMI with a thunderbolt adapter. When the AOC is unplugged it no longer recognizes the iMac signal and says no signal. I then have to get out an old 2007 MacBook and connect it to the AOC though the same HDMI cable but with a mini dvi adapter. The monitor recognizes it and I unplug it and hook it back up to my iMac and it then recognizes it. Any idea why this would happen?