Hit Ctrl+Alt+F1 at the blank screen to get you to a non-X terminal (tty1)
Login in with your username and password
Change to root with: sudo -i and enter your password
mkdir -p /run /run/lock
rm -rf /var/run /var/lock
ln -s /run /var
ln -s /run/lock /var
reboot
got this error after upgrading from 11.04 to 11.10 and couldn't boot up anymore.
did what was in this post and solved the problem:
http:// uksysadmin. wordpress. com/2011/ 10/14/upgrade- to-ubuntu- 11-10-problem- waiting- for-network- configuration- then-black- screen- solution/
Hit Ctrl+Alt+F1 at the blank screen to get you to a non-X terminal (tty1)
Login in with your username and password
Change to root with: sudo -i and enter your password
mkdir -p /run /run/lock
rm -rf /var/run /var/lock
ln -s /run /var
ln -s /run/lock /var
reboot