Why won't my mini dp to hdmi adapter work with my hdtv?

I recently bought a 2011 Macbook Pro 13" notebook, and the girl who sold it to me also sold me the Moshi mini display-port to HDMI adapter. She said all I would need to hook my laptop up to my Vizio LCD hdtv was that adapter and a regular HDMI cable. So I've now tried to hook them up no less than 10 times, and nothing still. The only thing that happens is, my laptop screen will turn blue and adjust the screen size as if it's trying to adjust to the TV, and my TV will say "retrieving data." So it looks like it's getting ready to connect, and then my computer screen will go back to normal, and my TV will then say either "not support" (whatever that means) or "no signal." Now I know there is nothing wrong with my macbook, since I have been able to hook it up to the TV with my friend's adapter. I thought she had the same adapter as me, but now that I really look at it, I think it's a display-port to VGA adapter. Plus the cable she uses is something other than an HDMI cable. Does anyone know why my adapter isn't working? Or is it possible that it's just faulty and I wasted my money? (Note: I've tried adjusting the resolution, display, etc, and nothing makes a difference).