This was happening to my wife's phone, always when charged to 100% overnight. The phone would try and switch itself on (regardless of being in the user-set power off period) and would cycle constantly between beginning to boot up, then vibrating, switching off. The only way around it was to hold the volume buttons, power etc in for a few seconds as described and it would go in test mode. (confusing as all in Chinese!) The battery charging symbol would appear but the percentage figure would be blank. Then repeat the process and the phone would start. The I remembered that we were not using the correct charger but a generic one for convenience as the correct one did not have a UK plug. I guessed that the generic charger was either not charging the phone quick enough (it's half the rate of the correct one) or it was not switching off when fully charged and overcharging the battery. There has been no further problems since using the correct charger.