Hope this helps.

1. Use the “Driver Manger” app in “System Settings” to select “nvidia-346” as the driver (not “nvidia-346-updates”). Click “Apply Changes”. Once the application is done processing nothing will happen (nothing will get installed, no prompt will appear, no message will be shown). Restart your computer (this is needed because NVIDIA's driver modify the kernel apparently and only a full system restart will cause the install to go through).

2. When Linux Mint launches after the restart, Cinnamon will be broken and only 2 of your monitors will work. Do not bother trying to fix Cinnamon this will just lead you down a path of useless installs.

3. Launch the “Terminal” app. This will be tricky when Cinnamon is broken because “Terminal” is mysteriously missing from the Applications list in the task bar! And right-clicking on the Desktop is also broken. The only way I've found to launch it is to use the shortcut created in Step 1 or use the keyboard shortcut Alt + F2. When a window pops up asking you to type a command to run - use "sudo ls" and check the "Use Terminal" checkbox. When a terminal launches, use the Ctrl+Shift+T keyboard shortcut to open a fresh terminal tab. Now you can close the original tab which is waiting for your sudo password. (You'll need to do this any time you want to launch a new terminal window).

4. In the terminal, run these commands:

   sudo apt-add-repository ppa:xorg-edgers sudo apt-get update sudo apt-get upgrade sudo apt-get install nvidia-346 nvidia-settings sudo apt-get --purge remove xserver-xorg-video-nouveau sudo apt-get autoremove

5. Reboot your computer. There is no UI button to do this so you'll need to run sudo reboot.

6. When the computer reboots things will still be broken. I'm not sure about steps 7 and 8. They may not be needed, but I did this while trying to figure out what's wrong so including them here just in case.

7. Next, run sudo gedit /etc/default/grub. In the editor, find the line that defines GRUB_CMDLINE_LINUX_DEFAULT and change it to:

   GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"

8. Now, in Terminal run this:

   sudo update-initramfs -u sudo update-grub2 sudo update-grub

9. Now use sudo gedit /etc/X11/xorg.conf to edit you X Config file. This step sucks because there's no nice GUI for editing this config file and if you make a mistake and corrupt this file - next time you reboot - you'll have no GUI anymore and possibly not even a working console. Make a back up of this file first. Once backed up, you'll want generally follow the things outlined here: https://www.martineve.com/2014/04/15/enabling-a-triple-head-3-monitor-setup-on-linux-mint-16-petra-with-two-nvidia-cards/ For me the changes I made were:

   • Make sure the "ServerLayout" section only defines Screen 0. There should be no lines defining "Screen 1". If you have such a line - remove it.
   • In the "Screen" section, make sure:
     • MultiGPU is Off
     • SLI is On
     • SLIMosaic is True
     • BaseMosaic is True

10. Reboot one last time. When you come back, Cinnamon should be working again and all your 3 monitors will be working again. Now you can use the NVIDIA Settings GUI to setup resolutions and screen positions/rotations, etc...

1. Use the “Driver Manger” app in “System Settings” to select “nvidia-346” as the driver (not “nvidia-346-updates”). Click “Apply Changes”. Once the application is done processing nothing will happen (nothing will get installed, no prompt will appear, no message will be shown). Restart your computer (this is needed because NVIDIA's driver modify the kernel apparently and only a full system restart will cause the install to go through).

2. When Linux Mint launches after the restart, Cinnamon will be broken and only 2 of your monitors will work. Do not bother trying to fix Cinnamon this will just lead you down a path of useless installs.

3. Launch the “Terminal” app. This will be tricky when Cinnamon is broken because “Terminal” is mysteriously missing from the Applications list in the task bar! And right-clicking on the Desktop is also broken. The only way I've found to launch it is to use the shortcut created in Step 1 or use the keyboard shortcut Alt + F2. When a window pops up asking you to type a command to run - use "sudo ls" and check the "Use Terminal" checkbox. When a terminal launches, use the Ctrl+Shift+T keyboard shortcut to open a fresh terminal tab. Now you can close the original tab which is waiting for your sudo password. (You'll need to do this any time you want to launch a new terminal window).

4. In the terminal, run these commands:

   sudo apt-add-repository ppa:xorg-edgers sudo apt-get update sudo apt-get upgrade sudo apt-get install nvidia-346 nvidia-settings sudo apt-get --purge remove xserver-xorg-video-nouveau sudo apt-get autoremove 

5. Reboot your computer. There is no UI button to do this so you'll need to run sudo reboot.

6. When the computer reboots things will still be broken. I'm not sure about steps 7 and 8. They may not be needed, but I did this while trying to figure out what's wrong so including them here just in case.

7. Next, run sudo gedit /etc/default/grub. In the editor, find the line that defines GRUB_CMDLINE_LINUX_DEFAULT and change it to:

   GRUB_CMDLINE_LINUX_DEFAULT="nomodeset" 

8. Now, in Terminal run this:

   sudo update-initramfs -u sudo update-grub2 sudo update-grub 

9. Now use sudo gedit /etc/X11/xorg.conf to edit you X Config file. This step sucks because there's no nice GUI for editing this config file and if you make a mistake and corrupt this file - next time you reboot - you'll have no GUI anymore and possibly not even a working console. Make a back up of this file first. Once backed up, you'll want generally follow the things outlined here: https://www.martineve.com/2014/04/15/enabling-a-triple-head-3-monitor-setup-on-linux-mint-16-petra-with-two-nvidia-cards/ For me the changes I made were:

   • Make sure the "ServerLayout" section only defines Screen 0. There should be no lines defining "Screen 1". If you have such a line - remove it.
   • In the "Screen" section, make sure:
     • MultiGPU is Off
     • SLI is On
     • SLIMosaic is True
     • BaseMosaic is True

10. Reboot one last time. When you come back, Cinnamon should be working again and all your 3 monitors will be working again. Now you can use the NVIDIA Settings GUI to setup resolutions and screen positions/rotations, etc...