Have you attempted to factory reset the device?

When you say it does not turn on, do you mean no power at all or it loads to the logo screen and shuts off after an error?

If you're able to power it on in the beginning logo, I would recommend factory reset. Keep in mind factory reset will erase everything.

Provide more details so we can determine if you should just flash the phone, which means reinstall the OS that may or may not lost all your files.