help GridPad 2050SL

[Choctaw Bob]

I just pulled my GridPad 2050SL out of the garage, fired it up, and it 
worked fine, for about 15 minutes.  Then the screen started to fade, 
adjusted contrast and brightness, worked for a few minutes then nothing, 
just the backlight.   Let it set for a few minutes, it fired up, but 
quickly back to the blank screen, with a quicker fade.

Any suggestions on what to check?  It has been in storage for the past 4 
years, no climate control, so anything is possible.  Probably heat 
related component failure or solder joint, but where to look.  Nothing 
found on the web.