When Graphics go wrong
From LXF Wiki
One of the most common problems seems to be when a kernel update breaks the installed video driver and inexperienced users cannot get a desktop back, but are left without a GUI and can't figure out how to re-install the graphics driver from the command line. It's a good idea to keep a copy of your diver in your /home/"username". Then all is needed is to boot to runlevel 3, login as root and install.
For Nvidia for example, once logged in as root cd /home/"username"
sh N (use <TAB> to auto complete)
If you want to enable graphics when you can't install a driver or say you have a laptop chipset or onboard. Login as root level3 and use this command
sax2 -r -m 0=vesa
reboot this should enable a display using vesa