On some systems with (older?) Nvidia video cards, Linux may be installed seemingly without problems. But after restarting the system, the screen stays black, with a blinking cursor, and the system does not respond to keystrokes. The cause is that those video cards do not work well with the default driver Nouveau. The solution is to install the proprietary Nivida drivers.

But how to do this when the system does not respond?

First restart the system, by pressing Ctrl X.

1. After the system has booted, i.e. after the BIOS has started, press and hold SHIFT. This will call the loader Grub to the foreground, and show the available operating systems.
   If you have installed Linux as dual boot with some other operating system, Grub will usually show on the screen automatically.
2. Choose one of the operating systems, usually the first, and press e to edit its options.
3. Find the line starting with linux, and containing the options quiet splash. Add nomodeset just before the quiet splash.
4. Restart the system by pressing Ctrl X.
   The system should now start with a visible screen, although with a low screen resolution.
5. Install the proprietary Nividia drivers:
   On Ubuntu choose Software and Updates / Additional Drivers; on Linux Mint, choose Menu / System / Drivers. Let it search for additional drivers. Choose the Nvidia driver with the highest version number, install it, and restart the system (Menu / Shutdown / Restart).

Source:
https://askubuntu.com/questions/38780/how-do-i-set-nomodeset-after-ive-already-installed-ubuntu
https://help.ubuntu.com/community/BinaryDriverHowto/Nvidia