Screens are controlled by ASPECT RATIO.
Monitors can have 4:3 16:9 and 16:10 ratios.
You are doing 1 of 3 things.
- You have a regular monitor and the tv and are duplicating the screen.
- You have a regular monitor and the TV and are extending the screen.
- You have just the tv connected.
Your video card has to have a screen resolution that meets the tv's ratio to have the tv take the full screen.
If your configuration is 1. the tv will only match the monitor resolution, so if you change the screen resolution, you may get bars on the monitor, and the tv will go wide screen.
if your configuration is 2. the tv is controlled independently and you can select it to change its resolution to an appropriate aspect resolution. *this requires that your video card gives you the correct screen resolution for your tv. not all displays will work.
If your configuration is 3. the tv is the only resolution that is being pushed and just adjust the resolution til the screen is filled in.
To adjust the screen resolution, right click on the desktop where there isnt an icon and select either Properties (windows xp) or Screen Resolution (windows vista, 7 and 8).
if you have 2 screens press the identify button and it will put a number on each screen. click the appropriate screen and go to the resolution dropdown below. Change, apply and if it doesn't look right, revert and try a different setting. if you try them all and it won't take up the full screen, then the video card can't push the video resolution your monitor wants.