I recently installed Ubuntu 14.04 dual-boot on a Lenovo T540. Every now and then, the display will freeze. It seems always preceded (but not necessarily caused) by some mouse I/O, never with keyboard I/O. It's only the display that is unresponsive as any ongoing video/music continues playing (yet the video obviously appear frozen now too). Keyboard I/O (and mouse I/O I think) continue working, as I can open a terminal and type in commands (but I can't see any of this happening).

The solution so far has been just to put my computer to sleep (by closing the lid). Upon awakening, the display is responsive again. Any keyboard actions I did while the display was unresponsive appear (such as anything I type in a terminal or document).

I've tried restarting Unity and Compiz while the screen is unresponsive, and that doesn't fix the issue. Restarting lightdm works but that kills all my applications, so is worse than just putting my computer to sleep.

Any ideas on what may be causing this or how to debug? Thanks!