Sounds like possible driver gremlins.
Download the latest drivers from the Nvidia site, do not install yet.
Download and install Driver Sweeper.
Uninstall all existing video drivers and reboot into Safe Mode. While rebooting, enter the BIOS setup and make sure the onboard video is deactivated (if there is any on your MB!).
In Safe Mode, run Driver Sweeper to remove all traces of the previous drivers. CAUTION! Examine every entry it is going to delete, and make sure it is not going to remove any system files.
Reboot and install the downloaded drivers.