I think I finally discovered the problem. While the computer was running someone turned off the overhead light and the computer went promptly to sleep and would not restart without cycling On, Sleep, On, Sleep as I tried to do work. The Sleep was only a few seconds and barely lit the screen and it went back to sleep. There was other lighting in the room so I missed the connection at first. I turned on the overhead light again for other reasons and "Voila" it started working again. It turns out that the keyboard backlight sensor is the culprit. The computer works O.K. when the Overhead light is on and goes to sleep when ANYTHING shades the light from the left hand speaker panel roughly at the top toward the clamshell hinge in the vicinity parallel to the USB port. i bought an LED 'reading lamp' that plugs into the USB port for power and curved the neck over to light the speaker panel area between the USB and the Tilde Key on the keyboard. As long as the LED light, or any decent reading level light is present e...