When powered on, fan spins loudly but no sounds

When I hit the power button on the computer nothing happens, other than the fan spinning up loudly. No other lights, and the monitor don't turn on. Can somebody please lend some insight? I just ordered a new pram battery as per some other answers I've read. I was thinking of replacing the logic board but want to know if anybody has anything else I can try out first. Also, can somebody please tell me how to disconnect the "TMDS video connector"? I don't want to break anything :s I've included a picture of the cable I'm talking about, in case I'm not referring to it correctly.