I have a RedMi 3S, bought about 2.5 years, unrooted.
I was using it earlier today - not doing anything fancy or strange (that I know of); but a while later, I wanted to use it again - but it was dark. Pressed the power button - nothing. Pressed it longer, to trigger a reboot - nothing. Connected the charger (just now) - and still nothing, not even the light indicating the battery is being charged.
What can be the cause of this occurring, and what can I / should I do about it?
Note: The phone did not suffer any physical trauma recently.