why is my non-rooted htc one m8 not starting up

[Android Central Question]

my device has been working fine a few days ago then suddenly it started shutting down itself but turned on when i press and hold power button. but now it doesn't even start up , it shuts down the moment htc logo shows up like when it doesnot have charge. but when i put it in charge it shows 100% in shutdown screen. i kept it charging for some time but it seems not working. please help me ...

 

[belodion]

It could be bad software, bad hardware, or just a bad battery.