Devices that are connected to your TV may have settings that affect the way the signal is output to your television. These devices may include:
Settings in these devices can affect the resolution and aspect ratio (4:3, 16:9) of the signal, which in turn can affect how the picture is displayed on the TV.
Generally, the settings of the device connected to your TV should be set to match the highest resolution your TV can accept. If you have a wide-screen TV, the aspect ratio of the device connected to the TV should be set to 16:9 if possible.