I've compiled many known methods there. It should help you and the thread starter. Happened with my 920 and 620 before.
And yes, if the phone looks dead, remove the battery (if removable) and insert it back and try connecting it to a USB port of your PC rather than the wall charger and let it be there for some hours. After that, try the methods in the link. See if it works.
what a suck. i update my lumia 620 to windows 10 but some problem but i am ok with it but now my nokia lumia 620 is stuck on gear screen keep restarting.when i connect to charger this happen plz help me:crying: