"nvidia-smi has failed because it couldn't communicate with the nvidia driver. Make sure that the latest nvidia driver is installed and running"

Hello
I was wondering if someone could help me with “nvidia-smi has failed because it couldn’t communicate with the nvidia driver”

I am using 64-bit PC desktop image Ubuntu version 20.04.5

I used:

sudo add-apt-repository ppa:graphics-drivers/ppa --yes
sudo apt update
sudo apt install nvidia-driver-470 

When I did that, I got

reading package lists... done
building dependency tree
reading state information... done
nvidia-driver-470 is already the newest version 470.161.03-0ubuntu0.20.04.1
0 upgraded 0 newly installed 0 to remove and 3 not upgraded

I have already used for 3 times:

sudo apt update
sudo reboot

But I still get

NVIDIA-SMI has failed because it couldn't communicate with the nvidia driver. Make sure that the latest nvidia driver is installed and running

what can possibly go wrong?