I think you just hit the nail on the head in the power kernel, if you can get the device back to workshop state your problems might be over unless you have a battery connection fault there so check where the battery connects to the 3 pins and in the battery you have 3 sprung connectors, if one of them had been opened too wide it will not make contact with the 3 pins on the device so worth a check.
Also check the 3 pins to see if anything loose there.