I will explain this fully and I'm sorry I didn't explain it fully because I was in rush...
Okay on the FMC, ( I set the IRS to ALign for L, C and R )... I got the IRS message to put the Ref Airport code.
On the FMC and I was on POS INIT page. I set YPAD ( Adelaide Australia ) on Ref Airport code and I click GPS POS to copy the codes and paste it toSET IRS POS. When it was set, I went back to the overhead and switch IRS to NAV for L, C and R.
The Primary Flight Display and the Navigation were functioning.
I went back to the FMC and change page to RTE 1. I put YPAD on Origin and YMML on Destination. The Navigation didn't show me the flight roots and airports. Even I tried to set up the runway for Departure and Arrival. Still it didn't show me on the Navigation Display.
It never happened on my Flight Simulator 2004 long time ago.