When it turns off it wont tun back on properly

Sometimes my phone will reset itself, or when it turns off it will not turn back on unless you reset to facory. It will show th M symbol and the android guy, and then he dies. and then it keeps repeating and repeating until you force reset to facory. it happened again today and now it is saying my battery is unknown and for a bit the sound was not working. what do i do??