You're using a GTX 980?
Did you use this with a previous monitor before?
It's possible that the display information is corrupted.
here's what you need to do.
1) download toastyX custom resolution utility and run the RESET-ALL.exe file, which is part of the package. Do not restart, howewver.
http://www.monitortests.com/forum/Thread-Custom-Resolution-Utility-CRU
The reset-all.exe will automatically take effect during the reboot.
2) download Display Driver Uninstaller, but don't install it just yet.
http://www.wagnardmobile.com/forums/
3) download the current Nvidia drivers.
4) uninstall your current Nvidia drivers through control panel or add/remove programs.
5) reboot to SAFE MODE.
6) run DDU through safe mode /install the package and let it clean the drivers.
You don't HAVE to run DDU in safe mode, but it's best.
7) reboot back to windows, run the Nvidia install package and install the current drivers.
Should be good to go.