Hi @nube
there is 50/50% chance, that this is '''hardware issue'''. But you can try:
* '''Force Reboot'''
** press and hold down the Power key for 10 seconds to restart it
If still having issue:
* Connect your OnePlus 6 to its charger regardless whether it responds or not
* Leave it connected to the charger for 10 minutes or so
* Press and hold the power key for 10 seconds or until the device boots up
If still having issue:
* '''Firmware reinstall'''
** Proceed via [https://forum.xda-developers.com/oneplus-6t/how-to/rom-stock-fastboot-roms-oneplus-6t-t3862516|xda]
If you still having issue, it’s really hardware problem. '''You must put your mobile into the service'''.
Regards