I'm running Ubuntu version 12.04 on Dell D620 laptop and have been for months. Everything has been working fine until a week ago, when suddenly every time I close the laptop and open it again, the program in use blinks each time I make a keystroke. Only the program blinks, not the whole screen. Rebooting solves the issue until I close the lid again. I have installed all the updates recommended in the package manager. Clues?