Trying to connect my macbook pro 13" to my TV with a mini displayport. but nothing happens?

Hi, I bought a Mini displayport a while ago. Now I am trying to connect my macbook pro 13" to my 42" TV with the mini displayport to HDMI.
All that happens, is my computer screen turns blue for 2 seconds and thats all. The TV screen says NO SIGNAL.
I've tried lots of combinations concerning connecting the cables and such. but with no luck.
Anyone gort any clue about what to do?
If not e want my money back from apple!