The most common cause of spontaneous disconnection of the phoneand is the fault of the battery or a bad connection between the battery contacts and the phone. This fault may be due to purchasing the initially defective goods, whether it's the phone or the battery, or the arrival of the deteriorating item for the reason of clogging of the contacts. You should in this case try to put another battery in the phone and test it for performance.Mechanical damage of the PCB – the second most common cause of disconnection of telephone. This can occur due to frequent crashes of the device. You can check the relevance of this reason, trying to bend the phone. It disable in this case means that you get the point.Sometimes a disconnection may occur due to failure of the software (firmware). For phones popular brands it is rare, however, the models imported from China, this fault is very common. Try to reset all data in phoneand factory settings and format memory and memory card. If this does not help, install the new firmware.Another reason might be hidden in corrosion of the mechanical parts of the phone. This fault often is the stay apparatus in the water (drop into water or pouring water). If this happens, the phone eventually just stop working.Also because of falling into the water may form oxidation on the contacts of the SIM card. In this case, clean them using alcohol.A significant reason it shut down the phoneand may be a fault with the power button. In this case you need to replace it.Sometimes the phone shuts off during a hard frost. In this case, it is sufficient for some time to hold the apparatus in a warm room, then turn on.