Some program couldn't identify my GPU, so I thought it might be a driver issue. I opened the Additional Drivers window and changed from open-source option (don't recall its name) to nVidia. I clicked Apply Changes. it downloaded something and then all set. I restarted.
Now every time I open Ubuntu it freezes after an almost fixed duration (less than a minute). I tried to open the Additional Drivers window and revert the changes, but it always freezes before I can do it.
I tried to open recovery mode, clicked resume, a bunch of logs with [ ok ] next to them fill the screen, then a black screen. That's it. Even after 10 minutes or so I just gave up and restarted.
When I click 'resume' in recovery mode I see a warning that goes something like:
... some graphics driver may fail, if that's the case, restart... Maybe that's related..
Is there a way to change the driver back without installing a fresh ubuntu? I use ubuntu 20.04 LTS.
Edit: My laptop's card is NVidia GT540M. it is probably legacy by now. The additional drivers window shows (the option I chose and caused the problem, even though it is the "recommended driver"):
Using NVIDIA driver metapackage from nvidia-driver-390 (proprietary, tested)
The open source version of the driver (that I am trying to go back to) is called:
X.Org X server - Nouveau display driver from xserver-xorg-video-nouveau
Edit2: The system freezes, but I can still move the mouse around for a while. I can't click anything and it stops recognizing keyboard commands. All I can do is hover the mouse (until it decides to freeze too after a while)