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 everything works O.K. but pass a finger under the LED and the computer goes to sleep.
I, too, got IStat widget and find it very comforting to know that my fans work on occasion, battery is at 65% life cycle and other comforting information. but Power was never the problem, Sleep settings were never the problem, Software or HD drive were never the issue.
I still have no way to fix it and although I was a Senior Chief Electronic Technician in the NAVY I am reluctant to go inside without detailed connectivity information about the power jack, Keyboard Backlight Sensor and the USB Port in that area.
Ron Brown