For some reason NVidia proprietary drivers seem to work badly on Linux. I had a similar issue with my laptop (HP Pavillion with a GeForce GTX 960M). In the end I solved it by installing a non-proprietary driver.
These steps should do the job: first clean up any eventual mess that there might be by doing
apt-get purge nvidia*
and then you can do the actual installation
apt-get install nvidia-387
After rebooting in principle you should obtain a non empty output to
lsmod | grep nvidia
but in my case it was empty and that was why it wasn't working. At the boot Linux wasn't loading the relevant modules. This was UEFI secure boot's fault. Apparently the secure boot didn't like the open source drivers and blocked them from being loaded. This can be fixed by going to the BIOS and disabling it (see here for a more thorough explanation https://askubuntu.com/a/762255).
If it still doesn't work you can try to look for these two possible issues:
Some other drivers are not blacklisted, e.g. nouveau (https://askubuntu.com/a/951892).
The file /etc/X11/xorg.conf isn't there. If so generate it with