Backup will not complete. ios 8.1.1

I recently changed from my iphone 5 to a iphone 6 plus, after i gotten the 6 plus i have not been able to back up the date on my 6 plus to my computer. The backup will just start and hang there, even if i left it there for a few hours. i am using a windows 7 computer, i tried deleting my old back ups and even reinstalled itunes but none of this helps. So if anyone could give me any suggestion on what to do next.