I am running 12.04 with an HD7970. I installed fglrx from AMD and it worked okay. Then Ubuntu prompted me to install updates (from software-center). After doing this, the PC only boots to a black screen called Chips tty1.
If I go to the recovery mode, all the options give me a blinking cursor (after a confirmation dialog), but when I press Ctrl+Alt+Del then they react (repair, gfx safe) and shortly after it reboots.
If I choose the normal boot, I get an orange
"Mountall: Plymouth disconnected".