This is a computer that has no data on it, it seems. Just the installation of Ubuntu plus some software. Best solution is to reinstall using 16.04. If it's an older computer or if it has little RAM, make sure you install Ubuntu Mate, and avoid anything with 3D desktops like Gnome3 and Unity. The Mate desktop makes a big difference in speed. You can make this change later if needed.
After installation, make sure you enable the SSH server, so you can login from another computer. You should enable UFW as well, the default firewall for Ubuntu. Enable port 22 to allow incoming SSH traffic. Then test this, so you know it works.
Reinstalling has another bonus. It increases your experience with Ubuntu, and makes sure the system is back to a fresh state. You have more control over what happened to it.
You can choose to use LVM during the installation process. This makes it possible to create snapshots of the system, making it possible to go back to a previous state if things go wrong.
NB: My solution doesn't give a solution to this specific problem. But to me you want your computer to work. Finding a solution that takes hours without any guarantee while reinstalling takes less than an hour - for me it's a no-brainer.
Unless of course the computer has data on it that is important and not backed up. In that case, use an Ubuntu live stick, and copy the data to an external disk and then reinstall.
Of course the same problem could appear after reinstallation. So make sure that SSH server works, and then you can work from there.