Will not power on, battery is charged, help please?

My business offers service and repair of gaming consoles, laptops, and mobile touch screen devices. Today we got a DSi xl (first time got one of these models) in the shop that won't power on. No lights when you press the power button, no flashing screen, nothing. I am assuming that the battery is charged because if you plug it in the charge light comes on for a while then turns off. If I unplug it and plug it back in, light comes on then goes off again. Also it will not power on when plugged in to the charger.

I took it apart and examined all the cables, solder joints, and boards; I cannot find any obvious physical defects or sign of liquid damage or impact damage. We don't have any spare parts for this device, I was thinking of ordering a new power board to start with, but before I do is there anything you can tell me that I might have overlooked or that I just dont know that could save me and the customer some time and money?

Thanks!