I will try to be as informative as possible of my issue since I don't know what logs might be helpful or where to find them.

I have ubuntu gnome 15.04 on a laptop, a dell inspiron 15 only 4 months old, with full disk encryption set up when I installed. I have been doing manual updates effectively biweekly with sudo apt-get update && sudo apt-get dist-upgrade . This has worked out well until about last week when I could not reboot post update, the machine locks up and becomes unresponsive on decryption. In order to boot now, I navigate into advanced settings in grub and choose 3.19.28 Generic rather than 3.19.30 Generic and everything seems to work just fine.

Thanks for the help.