Hi, I have been using my I phone 4 8Gb for the last few months and it was fine.. just now maybe 10 minutes back it shut down by itself and would n`t restart. Well the battery was around to 90%.I tried switching in on again but it is not starting up. Also tried plugging it into the charger.took out the Sim card and placed it back again. tried all... if anyone out there friends do know about it please do help me..well it was not in contact with anything harmful. it was just in my jacket pocket.