ok first make sure ur battery aint dead cause thats what it sounds like so get a fully charged battery connect ur phone to the pc and use RSD LITE not flash and backup and flash your backup and if u dont have one go to the downloads section an look for the firmware that exactly matchess your phone and flash it and you will be fine
I agree so you need to charge full battery use desktop charger or battery from another phone, then you must do testpoint to put phone in blank mode. If you flashed Simba's MP you shuld try to remove battery for about 5 sec, then put it back then press * and red button to enable dualboot. then connect USB cable and start RSD lite. If flash was sucess (or if you have dualboot) RSD will recognize phone as S Blank Neptune LTE2. If you haven't dualboot you need to do HW testpoint.
You need to dissasemble phone, connect USB cable connect testpoint cable (download and zoom in image to be able to view correct point, contact of small IC), connect battery and remove testpoint cable, battery hold connected.Then start RSD lite if testpoint is correct RSD will recognize phone as S blank Neptune LTE2.