I have the latest iMac that came out last summer (2011). I want to use my HD television to watch movies played on the iMac. I bought a cable that has the mini-display/thunderbolt connector, which I hooked into the thunderbolt/mini-display port on the computer, and the other end I hooked into the HDMI port on the television. Nothing. No signal. What do I need to do to make this work? Thanks in advance.