Is it my Macbook Pro or my Thunderbolt-HDMI adaptor that isn't working?

My Macbook Pro (running OSX Mountain Lion fully updated) wont connect to my Insigina HD TV set. This is a recent problem seeing as a week ago it would. I've used the HDMI cord with a PC and it worked, could it be that the thunderbolt-hdmi adaptor I bought a week ago died or is this a problem with my Macbook Pro?