I recently installed Ubuntu 14.04 on a new ThinkPad laptop as a dual boot with Windows 8. It has been running for a few days without issue. However, when I booted my computer today, it got stuck on the purple splash screen. I had to do a hard shut down and then booted in recovery mode, which seemed to work. I turned on verbose booting to see if I could figure out the issue, and then rebooted normally. It froze again; below is a screenshot at the point that it freezes. I didn't see anything out of the ordinary, other than the fact that it thinks that the brightness keys don't work (they have worked until now).

I'm at a loss as to what might have caused it to randomly start freezing. Any ideas on what might cause this, or anything else I can do to figure it out?

Edit: it's not just the brightness keys that don't work. The brightness slider in System Settings has disappeared entirely. I adjusted it just yesterday.

Edit again: It works (including brightness adjustments) when I boot with linux-image-3.16.0-34-generic, but not with the default linux-image-3.16.0-36-generic. Not sure if this update was just installed yesterday, and I still don't know what exactly is causing the hang-up.

screenshot from frozen state

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