Unlocked iPhone 4S won't back up now. How do I fix that?

My newly unlocked iPhone 4s won't back up to my computer with iTunes now. It says it's disconnected. How do I remedy that and keep the unlock?

I unlocked my phone following the instructions I was sent by Sprint, my carrier.

It seems like unlocking an iPhone can cause a variety of problems (or so I gather from trying to research this)