I had that same problem and just solve.
First of all, you must connect the iphone to computer restore mode. That you do it by turning off the phone and connecting the cable to the machine where you have installed itunes, holding the button START. There you a sign appears on itunes saying the iphone is restored. After this is done, you can recover your data from the most recent backup copy you've done (I hope you did). It's pretty tedious, but it's the only solution I could find.