Is the cable that you are using male to male VGA?
I assume you are using Apple's mini display to VGA converter. (does it work in other context? like trying to connect that computer to another display or projector).
Have you ask the TV specifically to try to display the signal that should be coming from the mac? (no auto detect but actually saying, TV try to display from this source). You can always try to contact the TV manufacture if they have any ideas to troubleshoot your display.
Whats the make/model/yr of the tv and yr of the mac?