Are you sure all settings on the macbook are as they should be? Does it show on other HDMI devices?
No answer on your other issues from me.
Kees
I'Ve just bought a samsung UE32F5000 TV and am frustrated by (1) the hdmi connection to my macbook doesn't appear to work (it says it's connected but not picture is transmitted!) (2) when I cannect my ext hard drive to the usb port and attempt to play movies they all come in one aspect ration which is 4.3 and is wrong (they're all widescreen). Oh and (3) it won't play mkv files - if I've got this right what should I convert my mkv files to - ago? mp4? vob?
Much obliged for any help

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic