How can I restore it? I went to enter KLAX as my departure airport and it said, NOT IN DATA BASE, #####! no major airports were in my FMC, so what happened?

This forum asks that you always sign your posts....The database is a set of text files in your .../Flight Simulator 9/FMCWP folder. Look in there (or drill down one), and you should have wpNavAPT.txt, wpNavAID.txt, wpNAVRTE.txt etc. Also, use the FMC index and goto IDENT to see the date of the AIRAC cycle data.These files can be obtained from www.navdata.at First, ensure you have the database then also check you have current SIDSTARS.There is an overview of this stuff in the PMDG OPS wiki library, article named SIDSTARS