dmesg is a CLI tool, you'll need to go into X Terminal to and type that in

So once you have enabled R&D mode and you have either USB connected or charger connected the device does not shutdown but as soon as you unplug the charger or USB cable the device shuts down?

Its somewhat relatively normal that your device blacks out after showing the initial Nokia logo and then afterwards you get 5 loading dots on the screen. I'm presuming the sound is for Nokia boot video? Also after the 5 loading dots, the screen will momentarily blank for maybe 5 seconds at most. Any longer than that then you may have issue with the device hardware-wise.