No mobile data access on Android phones

I just got a bueat new phone, the HTC Desire X, but one day two I suddenly had no internet access when on a mobile network (wifi was fine). The ‘Mobile Network’ setting was switch ON and toggling this switch didn’t do anything. I learned you have to check your APN (Access Point Name) settings by going into the Mobile network settings, then ‘Access Point Names’ and I saw that there was nothing listed there! Hit ‘Menu’ key and there’s an option to ‘Reset to defaults’. After I did this, my network operator’s settings appeared (Virgin Mobile Australia) and all was well!