iPhone 4 will not turn on, displays Apple logo when plugged in

Earlier today my girlfriend dropped her admittedly very out of date iPhone 4, the LCD did not sustain any noticeable damage but the back glass did.

The main problem however is that the phone will not turn on, which obviously implies internal damage, the strange part about this is that when connected to power it will display the apple logo but will never fully initialise, it is not detected by iTunes.

If I have to bring it to a repair shop I will but I would much rather repair it myself, I do have some experience repairing iPhones as I have replaced batteries and screens before at home.

Any help in figuring out what's wrong here and possibly how to fix it would be much appreciated.

Thanks in advance!

-Tenebraeon