Nvidia GPU not found (driver problem)

I was trying to use gpucomputing (through cuda) in matlab, but it couldn't find my nvidia GPU

I tried the steps outlined here, and found that the output of

lspci | grep -i nvidia 

includes

01:00.0 VGA compatible controller: NVIDIA Corporation GP107GL [Quadro P400] (rev a1)

but "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.

This seems to indicate that there is a driver problem. But via "software and updates", I have selected "using NVIDIA driver metapackage from nvidia-driver-470(proprietary)" which is the newest version available to me (earlier it was nouveau but I changed it), although there is still written "this device is using an alternative driver" I also tried downloading the linux-drivers directly from nvidia's website, but didn't finish the installation because I got a warning that it is better to use the Ubuntu one from software and updates.

From Ubuntu 18.04.3 LTS kernel 5.0.0-25-generic nvidia driver 440 not working with graphics card model GP107M GeForce GTX 1050 Mobile I saw that a problem could be with the driver header. But it seems that that was already in the latest version (of kernel version 5.8, the problem is there both when using kernel versions 5.8 and 5.12)

UPDATE: sudo lshw -c display gives

  *-display UNCLAIMED       
       description: VGA compatible controller
       product: GP107GL [Quadro P400]
       vendor: NVIDIA Corporation
       physical id: 0
       bus info: pci@0000:01:00.0
       version: a1
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress vga_controller cap_list
       configuration: latency=0
       resources: memory:a3000000-a3ffffff memory:90000000-9fffffff memory:a0000000-a1ffffff ioport:3000(size=128) memory:a4000000-a407ffff
  *-display
       description: VGA compatible controller
       product: Intel Corporation
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 05
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:145 memory:a2000000-a2ffffff memory:80000000-8fffffff ioport:4000(size=64) memory:c0000-dffff

UPDATE2: at startup, my computer gives this message, not sure if related