iphone 4 16GB white unlocked *faulty* !

The phone was in perfect working order until i dropped it and smashed the front glass, i purchased a new front and back for the phone which i then fitted. Put it all back together but now it seems the phone doesnt seem to start when the battery is connected but when i disconnect the battery the phone starts when plugged into the wall and home buttons arent working. Could be an easy fix but i give up with it lol to fiddly for me. Phone is sold as seen Other than the faults its in very good condition. Comes with box, usb and charger.