I was enroute to KJFK from KMIA in the B772 GE American. Before TOD the FMC goes blank and then the aircraft starts turning to the left off course. I tried to disable the autopilot, LNAV, VNAV and nothing worked. Displays also stopped NAV stopped moving even though the a/c was. I reloaded the a/c and it went back to default state. And I flew the rest of the way via autopilot. Any suggestions? Thanks.