How are you connecting the computer to the TV?

If you are using the VGA input on the TV then it may not support the Full HD (1920x1080) resolution, it's hard to tell without knowing the model number of your TV .
You may need to connect using a DVI to HDMI cable/converter to get the full resolution.

Also if the TV has a 1:1 pixel mapping mode you should probably turn this on to stop the TV applying it's picture processing to everything.