trouble with external moniter

I have a new macbook with mini displayport. I have purchased a mini displayport to hdmi adapter and have managed on only 1 occation to get the computer to recognize the television. I followed one of the other posts and hooked up the coumpter to a power adapter and that seemed to solve the problem once, now I can seem to get it to work again. Is there a sequence of powering up that I am missing?