Fading into a black screen

I have same problem. STL100-1, made in Mexico. Tried autoloaders, web updates but no solution. Only thing I have noticed that it boots up okay if cooled or chilled by keeping in front of an A.C. and remains okay for days together if used only for voice calls. Try data, net or YouTube, the problem resurfaces again. Chilling it again boots it up normally. Back heats up a little just after these blackouts. Backlight stays .