I cannot install TITAN RTX driver

Hello, I’m usign titan rtx model on Ubuntu 16.04 LTS

I’ve downloaded the driver file :

and typed

sh ./NVIDIA-Linux-x86_64-440.100.run

It showed the installation guide, but it said like this:
There appears to already be a driver installed on your system (version: 440.100). As part of installing this driver (version: 440.100), the existing driver will be
uninstalled. Are you sure you want to continue?

So, I canceled installation.

but when I command nvidia-smi,
root@cosmos-System-Product-Name:/home/cosmos# nvidia-smi
NVIDIA-SMI has failed because it couldn’t communicate with the NVIDIA driver. Make sure that the latest NVIDIA driver is installed and running.

was shown. How can I solve this problem? Thank you.

In general, is there an urgent reason you’re using Ubuntu 16.04? That version doesn’t really work well anmore when it comes to nvidia, so I’d recommend to upgrade to at least 18.04.
Also, the .run installer shouldn’t be used on distributions like Ubuntu which provide a packaged driver.