unexpected shut downs

I have a iphone 5c with ios 8.3. It has been turning off unexpectedly despite having a full battery. I can have 100% . When it shuts down the battery life drops to 10%. The screen has spots that can best be described as a constilation. My microphone and front camera doesn't work. I've tried to reset it by pressing the home button & power button. It hasn't been dropped on the floor or into water.