Unfortunatly that's probably your only option, you've tried just about
everything else, though it wouldn't hurt to leave the cmos battery out for a
bit like you did. You could check for bulging or leaking electrolytic
capacitors on the motherboard but other than that it's probably not
economical to repair unless you can find a working one with a broken screen.

Some of those have a reset button as I recall. Usually a small hole somewhere on
the bottom with a tact switch inside. Might be worth a look.

Alan Harriman