HDMI to VGA cables only work one way, to send video *from* HDMI, *to* VGA. You're probably trying to use it the other way around, to connect your computer's VGA output to your TV's HDMI input - but it won't do anything if you hook it up that way.
To go the other way, you need a more expensive VGA to HDMI converter box, or instead (if your TV has a VGA input), get a long VGA cable, they make some that also include audio connectors at either end.
