Tried another computer head yet to see if it will sync? I hate to even suggest doing it, but a re-set or formatting the 520 and re-loading the firmware (Ver 9.1 is the current version) might help, but I doubt it.
PT can rebuild it for $350'ish or spend $330-$700 on a new hub and build up a new rear wheel.
Or...spend lots more on new pedals, crank arm, crankset or new wheels. You really wanted a new pair of PT carbon race wheels, anyway...right?