Hi i bought a mini dvi to video adaptor from apple. I also bought a cable to go with (yellow tulip) so i could use my tv for watching movies since it is bigger then my 17'' iMac. but when i plug it al in. and have the tv on the correct channel it doesnt work properly. i do get the blue colour of my desktop and thats it. if i go to front row the tv screen goes black but thats it. what am i doing wrong help please?