What worked for me is I unplugged firestick power cord. Wait about 2mins plug firestick in different hdmi. Plug your power cord plug back in. Hope it turns on for you.
All these videos are useless af. If you are already stuck on the boot screen none of these commands work. You need an OTG adapter and using a keyboard to send proper commands to during logo boot to disable services which in turn boots the unit. Nothing with the remote will work from the logo screen...