Using a 15foot VGA cable, trying to hook up my laptop to my TV, at first I had mirrored images just fine. Then I went to make the TV my main display, but when I did so, I chose a resolution that isn't supported by the TV. So now when I plug it in, the TV goes black screen and says not supported, but I cannot see anything on the laptop to change the resolution back lower.
You should be able to toggle back to mirrored mode (usually a keyboard shortcut) to get display back on your laptop.