Hey, so I brought a samsung galaxy ace GT-s5830 second hand. When I first started using it, it was fine. After about 5 hrs it would randomly vibrate then sort of restart. It would go black then go straight back to the screen where I unlock it as though i had put it to sleep. But it happens when I've put it down and doing nothing and when I'm txting or on facebook. Sometimes when it vibrates it will show a flash of red that looks like the vodafone symbol then straight to the screen. Would really appreciate any help. I've tried resetting the phone and it still does it. I've also got android booster to manage what apps are open. Would really appreciate any help???