Why isn't HDMI iMac 2011 working

Hi. I have an HDTV, an HDMI cord, and a HDMI -> thundebolt adapter. I plug this in to my 2013 MBA and it works fine, but when I plug it into my iMac, nothing happens.


Why?

Do I need a DVI -> HDMI adapter (I already have one for my dual monitor, so it would only be 5$ for the adapter.

Thanks for the help .

nobody?

also posted on reddit, etc will update if resolved