Are you using DVI or HDMI?
Some monitors/HDTV's require you to setup HDMI settings in the HDTV section of the control panel (such as 1080p_NTSC@60Hz) so try DVI instead.
Other things:
1) In the NVidia Control Panel, go to "adjust desktop size and position" then change
a) Scaling to the GPU (not monitor), and
b) Scaling to Aspect Ratio (if not already)
In this mode, the video signal sent to the Monitor is always 1920x1080 (if that's your monitor's native resolution). For example, if you chose a game to be 1024x768 then then the graphics card does all the stretching scaling etc before sending out the proper 1920x1080 signal.
If MONITOR was chosen instead of GPU then a 1024x768 signal would have been sent out so you'd need to have the...