After I installed FSX to the same PC as FS2004 , in my PMDG 737 FMC if I choose a runway for arrival it does not line up with the runwayin the sim .Any ideas plse

This problem came up recently with airac cycle 0608. This may not be your problem, but just wanted to mention it as a possiblity. The fix is to either get current airac data (0611) from navigraph or download 0610 which is still free and relatively current.