ok i am an idiot, had an ipad 2 and 3 here, didnt even think about the ipad turning on while i was cleaning the broken glass i must have hit the power button :(,
anyway the solution to remedy an lcd screen not working after you repaired the digitizer is correct.
need to shine some light (better in a dark room) onto the ipad and you will see the pad is actually on, hold the power button down and up the top of the screen normal "slide to switch off".
power up the device and shazam, it works :)