Last time I restarted my computer, I could not get Ubuntu to load; the screen would either go black, or would hang at the purple screen indefinitely. I have had some graphics problems in the past, but had put 'nomodeset' after 'quiet splash' in the grub command line, which at least let Ubuntu load. That doesn't work now, and doesn't work if I remove it.
I looked up some answers, such as this one: Purple start screen - no splash screen However, when I enter the root in recovery mode in grub, I always get errors when I run those command lines and it won't let me modify the files.
Also, if I run in recovery mode and then choose 'resume normal boot', it will continue. But instead of getting a usual interface, I get a black screen that asks for my username and password. I enter these, and it tells me I'm in Ubuntu 12.04, but I'm still on a black screen with texts. It also informs me that there are updates to install. When I use the command 'sudo apt-get update', it starts to retrieve the information, but then the screen goes blank after a couple of seconds and I can't do anything anymore.