Before you reinstall your Ubuntu, check out this tip:
If you changed something on your Linux configuration regarding video you can easily solve your problem returning your old /etc/X11/xorg.conf
In most cases we do not have a backup of this file until we need it. In this case you can reconfigure your system with this command:
sudo dpkg-reconfigure xserver-xorg
Just follow the screen instructions. A Vesa video work fine for most boards in an emergency.