What connection are you using...HDMI, DVI, VGA(blue connector with thumb screws on each end)?
Also, did this work ok before?
If so, what has been done since the last time it worked ok?
JQ
Edit: Ok, I see the answer to my questions.
Sounds like an installation problem...
1.. uninstall the drivers for your GFX. use driver sweeper to get them all.
2.. restart the system and it will install generic windows divers.
3.. after system is fully loaded, check your resolution and see if you can move up to your native res.
4.. install the NVidia drivers and this should fix the issue with the monitor and res problem.
Let us know if it worked.
JQ