I was running Ubuntu 12.04 LTS for 64 bit systems on a dual boot custom computer with Windows 7. It was functioning normally for at least 3 days before I noticed that Youtube videos were flickering on my screen in Chromium. My first thought was to update flash, and since flash comes with the latest version of chrome, I tried updating my Chromium installation. At first I tried using the Chromium Updater Extension, but it didn't solve the problem. It was somewhere around this time that Chromium stopped opening completely. I then tried uninstalling and reinstalling Chromium, but it still wouldn't open. I tried running the program from the command line, but got a message involving "libudev.so.0" being missing from the operating system. I believe after this I had to leave so I shut down the computer.
The next day, I tried loading the Ubuntu installation, only to see that it was stuck on the purple screen. After waiting a while, I tried restarting it and loading it again. This time, it only booted to a black screen with a blinking line at the top left of the screen, much like a terminal window. I tried removing all the non essential USB devices but it still wouldn't boot.
I did attempt to use the Boot-Repair Graphical Tool, but it said that it encoutered an error and gave me this link: http://paste.ubuntu.com/7306456/ . Ubuntu still won't boot at this point, and I'd rather not have to reinstall it a third time. I did try Repairing Grub2 via the live CD terminal as accoridng to this page: https://help.ubuntu.com/community/Grub2/Installing#via_the_LiveCD_terminal , but i'm a bit nervous about removing the Grub entirely. Won't that make it difficult for me to boot windows? Also, I can't remember exactly when but I got that same message about libudev.so.0 being missing again at some point when trying to boot. Probably after using Boot-Repair.
April 23 - I did try enabling boot messages to see if anything useful came up, and I got two messages at the very end that looked important.
ureadahead main process (312) terminated with status 5
mountall main process (319) terminated with status 127
I did try looking up solutions, but the ones I found sounded very sketchy and all over the place.