Flat screen resolution issue

When i connect my tv (19" Sansui LCD) to my laptop and select "Duplicate on both monitors" It works perfectly fine at 1366x768 resolution. When i select "Only show on 2" to turn my computer monitor off, it totally kills the resolution on my tv to something like 1024x768, and then stretches it to the wide screen. But i of course do not need 2 monitors running. How can i turn my laptop off without it killing my resolution?

Please note:
The monitor works perfectly while duplicated, it does not work while only on by itself. I do not see a reason why turning my computer monitor off should make the tv not work.

Thanks for help!