My iphone 6 will not turn on after charging it fully and trying hard start

Hello serah272,

Here are a few ways to jump-start your iPhone 6

• • Performing a DFU Reset - DFU mode lets the device interface with iTunes, update the firmware and restore the OS without automatically installing the last downloaded version. It's useful for installing older versions of iOS if a beta persistently hangs your phone, or if an hardware/software update were to go wrong.
  • Performing a Soft Reset - A soft reset is a restart of a device, such as a smartphone, tablet, laptop, the action closes applications and clears any data in RAM (random access memory), a soft reset consists of restarting as opposed to shutting down completely and starting the computer again.
  • Contacting apple about a dead battery / battery replacement - Since I have no background knowledge of what the case is, I recommend contacting apple first, letting them decide what it may be and apple support making a official replacement repair (depending on what the case may be)

I wish you the of luck!

Good-day <3

Old device and maybe the battery has failed.

Have it examined.