I'm assuming you're using a dvi/hdmi connection? If so, then you need to turn off over-scan. This is either done through your tv, video card drivers or a combination of both. And it's not always obvious where you need to go. Good luck on that. Your computer should be picking up your recommended resolution. These days it's generally 1920x1080 or 1280x720. Some tvs use an odd resolution between the two.

If you are using an analog input (vga, component, etc) you're probably not going to be able to disable over-scan. Analog connections are not recommended for serious computer use.