How to get my iPhone 4 to sync to iTunes?

I've had my phone for about 2 months. When I first plugged it into my laptop, it synced perfectly. Now my iTunes won't even register that it is plugged in.

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Does your computer notice the iPhone at all? Even aside from iTunes, the iPhone should show up in "my computer" as a camera. Does it charge? If neither of these things happen, there might be a problem with the cable or the connection at either end. Which USB port are you using? Back are the best. Hubs aren't optimal.

If the iPhone shows up, it may be an issue with iTunes. Try exiting and restarting iTunes while the iPhone is connected; try rebooting - that's what I do on the few occasions this happens to me with my ipod touch 3.