If you can open it and see if it has water damage do it.If not try to swap the battery.If this does not help,go to a phone shop or apple.But before you go check the phone's imei so it does not have Icloud on it.Go here:
You must login or register to view this content. enter the imei number which you will find in the bottom of the phone.
Please note: This is an official Apple website.
LE: For parts or not working means a device that is only sold for spare parts(or if you think you got the knowledge to repair it for repairs)