I replaced my surface pro 2 screen/digitizer assembly as it was damaged. The unit was working prior to the replacement. Once the new screen was installed I tried to switch on the unit to check the screen was working. I charged it overnight. The unit will not switch on. The unit will not boot as it seems as if it is not getting power. I have tried holding down the power button for 30 sec and holding the power and volume up button to 15 secs, neither work. Please could somebody help.