I'm base user - all my advises may make it worse for you. Only take actions that you understand.
>Even when I tried to press it for over 30s, I can't see the green light.
Not sure how, but i was there and got my kindle back to work. Are you able to get into diagnose mode? Are you able to access the Kindle via USB?
Did you change scripts before the kindle broke? If so - you might want to revert that changes with a script via usb, that fixed a lot for me, together with the factory_reset.
Make sure you don't mess up any further, better think twice. (I'm to nervous once in a while :-)
PS: Any good advises how to make my /tmp/root/authorized_keys persistent? Didn't see something like /etc/rc.local and don't need another unbootable situation right now :-)