It is possible that the screen backlighting could be going bad. But a bad power source could also cause problems. You just gotta narrow down on the possible causes and then figure out what to do from there. As others suggested, try using a different AC outlet. Or try swapping the power supply with a different one. You can even go as far as trying it out at someone else's house. It is summer and many people are running their air conditioners. And in the past I've seen air conditioners cause fluctuations on the power line.