I followed directions found here:
FAQ - PMDG B777/747/737NGXu FMC Runways Not Available - FMS Data / FAQ - Navigraph
I then removed ALL files inside the PMDG/NAVADATA folder except for airport.dat.
I then re-ran the FMC installer and I now have a full set of STARs and runways.
I hope this helps someone in future that may need it! 
All is well now.