@alexdon is on to something here, it does sound like the demo mode is activated in your device as it goes back to default when you connect the charger to the device.
Is this something that has started to occur very recently or has it been like this since you received the device?
If it's only the demo mode being activated, try opening up the Phone application and type in *#*#73556673#*#*. You should now end up at the home screen again and the demo mode should be disabled. You can also go to Settings > Security > Device Administrator and uncheck the Retail or Demo Mode option. This will remove Demo/Retail Mode from device.