iPhone no longer syncs automatically when connected to PC
I'm guessing (since you do not state this in your question) that iTunes tells you something along the lines of "This iPhone has not been synced with this computer before so now I have to erase everything on your phone." This is because after the reformat, your iPhone and computer no longer recognise each other because the computer is seen as a different computer.

If this is the case, I don't think you have any choice but to setup your phone anew. Fortunately, you can at least transfer your iPhone content to your computer before you do this by following the instructions at iTunes Store: Transferring purchases from your iOS device or iPod to a computer and/or Downloading past purchases from the App Store, iBookstore, and iTunes Store. I hope this answers your question, but like I implied earlier: some more information would be nice :-)