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try clicking the apple logo in the upper left corner of the screen to access your System Preferences. Go to Displays and click "Find Displays" i think is what its called. See if that puts the correct display on your tv screen. It's strange that it isn't just automatically displaying the correct video if it's displaying the screen saver.
For my macbook I have a mini-dvd to video cable and that works just fine BUT its the least clear input. VGA and HDMI are obviously better. ANYWAY, see if the displays area has anything that helps it to work