Help! My phone will not sync and I can't download music or apps!!

I have been using my iphone and I have not had any trouble with it before I love my phone! But just here recently when I hook my phone up to the computer it will charge but it always pops up that the device has malfunctioned and will not let me sync with itunes?? I have called apple and they have sent me emails to help with the issue but nothing works! All I can do is charge my phone, I can't dowmload apps or music! What do I do????