You may encounter a blank screen after boot in ubuntu. This will be due to some update of certain packages.
Follow these steps to correct the problem.
1. Select recovery mode from the boot menu.
2. Select login as root from the menu in recovery mode.
3. Type this at the prompt
# sudo apt-get remove xorg-driver-fglrx
# sudo dpkg-reconfigure -phigh xserver-xorg
5. Now select Resume normal boot from the menu.
Every thing should be OK by now.
Please comment about your experience.