You need to connect a keyboard directly to your core, not try to ssh into the core remotely as there is no networking in runlevel 1 or recovery mode. Now reboot your core - when the GRUB boot menu comes up, hit ESC and choose the recovery console.
This will give you a terminal at runlevel 1 so you can install the drivers - obviously, make sure you have downloaded the drivers somewhere local before doing this!
Now follow the instructions on the wiki in the Display Drivers article. But essentially you just run the nVidia .run file and follow the instructions.