If its a new hard drive you will need to load windows onto it. If it had Windows 7 on it and it stopped working than it could be the hard drive failed.
unless you have to move the charger around for it to say that it is charging, you will only have to replace the battery. The battery (at least for the Sero 7) is relatively complicated to replace. by that it needs to be soldered into place and likewise. hope i could help
The only thing i can think of is either the cord is broken, or you didnt install the new lightning port in correctly or didnt connect it all the way to the logic board.