Hoping that this should be a quick answer. I have a thunderbolt to HDMI from the back of my iMac to my TV. It works just fine. Turned off mirror so I can watch videos on my TV but still use Mac. However when I use iTunes in full screen mode on my TV, a gray screen slides over and my iMac display goes black/blank. The image is perfect on my TV, but just black on my Mac. What am I missing. I should have prefaced that I'm a brand new Mac user. Thanks in advance.