have you updated it to 4.1.1 yet (look in settings, about device)?
If so, you probably need to factory reset (in settings, storage)
Itl wipe ALL data from your phone though like new but getting a replacement does the same
Sorry i just reread and its been dodgy since day one?
Id try the factory reset (very annoying but when you start it again, if youre on wifi, it should download all your apps again or just return it as a dud
If youre gona return it, download KIES for your computer, back up everything then restore it to new phone, i just hope it isnt a dodgy app or u could end up with same problem.... if so.. its factory reset time
MERRY XMAS!!!X
Unbranded international s3 with Official 4.1.2 JB. Paisley, Slotland, Western Europe :beer: