The lack of Additional Drivers is a known bug in Ubuntu 14.04 (I'm guessing you're running that). I ran into this issue myself with my GTX 750 Ti.
Unless you need the performance boost for gaming, the default Nouveau drivers are just fine. However, if you do want the performance there are multiple methods to resolving this.
Download & install via the .run file from NVIDIA.
You'll need to download the newest NVIDIA stable driver from here and save it somewhere you'll remember - your home directory is a good choice.
Note, make sure you've saved and closed all your applications before continuing any further, because you're going to kill the display manager/X server and thus any applications running.
Once the driver has downloaded, you'll need to go into a TTY. You can do this via Ctrl+Alt+F1. Once you've got a text console, you need to log in with your username and password.
Once you've logged in on the TTY you need to get the same directory as the downloaded .run file. It'll be in your downloads folder most likely. Run cd ~/Downloads
.
Next, you'll need to kill the display manager/X server. You can accomplish this via running sudo killall lightdm
.
Finally, run sudo chmod +x ./NVIDIA-Linux-x86_64-340.32.run && sudo ./NVIDIA-Linux-x86_64-340.32.run
.
You'll have to accept a few things here and there. If you get an error saying that the pre-installation script failed, go ahead and ignore that. I got the exact same error and there's no actual problem.
Once the script completes, you'll need to run sudo reboot
and you should boot into an NVIDIA-drivers-driven system!
Use the Xorg-Edgers PPA Drivers:
This seems to be the most common answer, but it's probably not the best choice, because the drivers from this PPA are known to cause various graphical issues like black screens and whatnot.
If the first method doesn't work, go ahead and run the following commands:
sudo add-apt-repository ppa:xorg-edgers/ppa -y
sudo apt-get update
sudo apt-get install nvidia-340
sudo reboot
This will add the Xorg-Edgers PPA and install the latest NVIDIA 340 drivers. Once you reboot you can remove, or keep the PPA - that's up to you.