External Monitor Software Problems

Hey all,
I just recently bought all the hardware to hook my Macbook up to my TV (soniq 42' plasma) and use it as a external monitor, but I seem to be having a few issues.
I'm able use the TV as the external monitor when running windows, but when i switch back to leopard there is no signal to the TV and so no picture. However if i connect the Macbook to a regular PC monitor it works no problem in Mac OS.
Can anyone help me resolve this problem?
Cheers

I believe there is a "Detect Displays" option in the Displays System Preference. Did you try that?

Yeah I have adjusted the display settings and used the "detect display" option, still no picture.

What interface are you connecting to on the TV? VGA, DVI, HDMI. How long is the cable? Is your TV on the right input? Has it worked with anything else?

The interface i'm connecting to is a VGA and the cable to the TV is about 3m, every time i have used it, it has been on the correct input (VGA). I connected a PC laptop to the TV and it projected windows OS fine, so i tried the mac and nothing would come up. However if i run vista on macbook then it projects on the TV, thats why i'm thinking it might be a mac OS problem.