So I'm on my phone and the screen suddenly goes black. I've just tried to turn it on numerous times and it's just buzzing and doing nothing. It won't light up or anything. I tried it about 5 minutes ago and the phone started up but as it asked me to enter my sim pin, it shut off again and won't let me turn it on. What do I do? I've had the phone a year, it's a Samsung galaxy ace 2. I'm thinking of going to the shop tomorrow and demanding a new phone because every phone I seem to get has some kind of problem. It has had no damage at all. I was literally in the middle of a text, it was fully charged and it shut off.