since you said trying nvidia-driver-390 I can suggest you try some solutions. The first one is trying to get the drivers from Software & Updates, under the "aditional drivers" tab.
In my case I already installed Ubuntu with the proprietary drivers, but you could try selecting the first option: proprietary, tested.
If it doesn't work you could try to purge any existing Nvidia drivers and reinstall them, you can do this by typing this on your terminal:
sudo apt-get remove --purge '^nvidia-.*'
Please be aware there's a dependency between one of the packages that will be removed and ubuntu-desktop, therefore you may as well need:
sudo apt-get install ubuntu-desktop
Then try to reinstall them via terminal, and search for the adequate drivers using:
apt search nvidia-driver
If nothing works, since you already tried Arch, you could perhaps try installing Ubuntu, it supported my card out of the box, or Fedora, which is RPM based, it has good out of the box support for Nvidia as well.
Now as a personal recommendation since your system is already broken, the Ubuntu installer includes Nvidia drivers, so I suggest you go for it instead this time, since you can change to a flavor anytime with
sudo apt-get install kubuntu-desktop
I don't know if the installers for the flavors are different, but Ubuntu's supported my card, it's what I can suggest.
Good luck!
