Ok yesterday, my Lumia 920 kept rebooting powering itself off numerous times, I decided to do a device reset because I had no idea what was the cause, maybe an app but had so many loaded & didn’t have the time to try and go through them 1 by 1. I did a device reset & all seemed well until I had the spinning gears for about 25- 30 minutes. I waited and waited and then knew I was in trouble over an hr had passed. I spoke to @jjklee because I know he had the same issue and knew the method to resolve it but to no avail, it didn’t work. I then contacted from @NokiaCareus she told me the same method as @jjklee but I was doing something wrong. So I will post the exact steps on how to revive your Lumia 920 when you are stuck with spinning gears.
1- Wait till phone battery completely dies
2- Remove Sim
3- Put phone on wall charger
4-Let charger charge the phone and turn itself on automatically (do not power it on Manually)
This is all I was told to do & it worked, the issue I was having was that I kept powering it on manually & was met with spinning gears each time. I then said the heck with let battery Die and put it on charger, when it had enough juice to power itself on I saw the nokia logo screen the the wp8 splash screen & new all was good. Please let us know if this works for you & hopefully you never have to try it.