There are two ways to adjust the picture.
One is with the television - which it sounds as if you have tried with little success.
The other is the source - the unit providing the picture, and how THAT sends the signal. Many cable boxes, DVD players, Blu-Ray players and other peripherals ALSO have a menu where you can adjust the aspect ratio. If you're looking for a widescreen picture as the final result, set the TV on 16x9, and then adjust the menu settings of the other unit.
Does that help?
I can't seem to get the full top and bottom of the picture to show on my 550 series LCD. it's especially noticeable when a sporting event is on and the game data and/or scores that are always shown at the top or bottom of the screen are cut in half or are barely noticeable at all.
I've played with the settings but can't fix the problem. Any ideas?