Quoted from LTG:Having batteries in is good. Facing the right direction is better. Battery power actually getting onto the CPU is best.
One of the three is lacking. Grab a meter and work your way backwards. I'd bet on failed battery holder.
LTG : )
I've had the solder joint break on the back side of board mounted battery holders when changing batteries. That could be the problem. Don't let the force of pulling a battery out flex the board!