Q: An Original IPSW File For IPhone 5?

My IPhone 5 Is having a glitch where as I charge it there is just a charging screen and then the apple logo, and it keeps on doing that, I've already held down space and tried to get itunes to factory reset it, but I would always get an error 21 code, now it is looking for an IPSW file for me to restore the iphone 5 with, I'm wondering if there is anyway to get the original  file that would have resulted from a factory reset.