why is there a flashing green light on my htc one m7 when my phone is off

[AC Question]

I was locked up for two years and when my htc was completely dead I finally got it to start charging again but it still won't turn on it vibrates when I hit the power button but doesn't turn on and there's a green flashing light while it's off I know it's not a notification because there is no service

 

[B. Diddy]

Welcome to Android Central! A battery that hasn't been charged for 2 years might be completely dead. Leave it plugged into a wall outlet for at least 12 hours undisturbed, then try powering on by pressing and holding Power for 10-15 seconds to see if it turns on. If it doesn't, you'd probably have to bring it to a repair shop to see if they can replace the battery.