Error: NVIDIA-SMI has failed because it couldn't communicate with the NVIDIA driver

The issue might due to a confirmed "bug" in 4.4.0-116 patch. I ran into the same issue with nvidia-390. If you still want to use a newer version of Nvidia-driver, I followed the instructions here and managed to solve the problem. In general, use the following steps:

1. If you cannot login to the desktop and fall into to the fail-loop, press ctrl + alt + F1 to login into the command line mode.
2. Check if the version of gcc is outdated, if so, update it: gcc --version
3. If the gcc version is 5+, uninstall the nvidia driver first: sudo apt-get remove nvidia-390
4. Purge the 4.4.0-116 kernel: sudo apt-get purge linux-headers-4.4.0-116 linux-headers-4.4.0-116-generic linux-image-4.4.0-116-generic linux-image-extra-4.4.0-116-generic linux-signed-image-4.4.0-116-generic
5. Reinstall the kernel: sudo apt-get install linux-generic linux-signed-generic
6. Reinstall the nvidia-390: sudo apt-get install nvidia-390
7. Check if the problem is solved by modinfo nvidia-390 -k 4.4.0-116-generic | grep vermagic, make sure retpoline shows up this time
8. Reboot: sudo reboot

Hope this works for you and other people who run into the same issue. The post in the forum saved my weekend.

Try

1. Download the driver from here
2. sudo apt-get purge nvidia* - To remove your current installations
3. dpkg -i nvidia-diag-driver-local-repo-ubuntu1604_375.66-1_amd64.deb - installing what you downloaded earlier
4. sudo apt-get update
5. sudo apt-get install cuda-drivers

After this, go on and reboot your computer. When it's up again, the nvidia-smi command should run smoothly