Ubuntu 16.04 - NVIDIA driver black screen

An NVIDIA keel module 'nvidia' appears to already be loaded in your
keel. This may be because it is in use (for example, by an X
server, a CUDA program, or the NVIDIA Persistence Daemon), but this
may also happen if your keel was configured without support for
module unloading. Please be sure to exit any programs that may be
using the GPU(s) before attempting to upgrade your driver. If no
GPU-based programs are ruing, you know that your keel supports
module unloading, and you still receive this message, then an error
may have occured that has corrupted an NVIDIA keel module's usage
count, for which the simplest remedy is to reboot your computer.