Just to add to this thread, just had the same thing happen to me. FMC went blank and then all systems unresponsive.
In my case it was caused when I attempted to divert to my alternate (EBBR). I clicked EBBR at the end of my flightplan, selected my approach and then hit the insert button and that is when the freeze happened.
Using the latest version of the A300F (GE), latest nav data from Navigraph.