I am attempting to start up 777 from C&D in the MSFS Pmdg aircraft selection under PMDG 777. The cockpit is all dark , I go to the upper panel and all switches are on., what is needed after that?  BTW, if the switch is showing ON, gdoes that mean it IS ON or that it has to be pushed to turn it on?..Thanks from this 89 yr old .

Given that the pmdg 777 is not on msfs yet,i'm assuming you are refering to the  fsx or p3d version. 

In answer to your question though , have you made sure both your batteries are on? Following that either start the apu or power the aircraft from a gpu

Go to the FMC and select "FS actions", there should be an item called "connect GPU (Ground Power Unit). After that, check that the battery switch is on, located on the left of the the overhead panel, and that primary and secondary ext power are set on, right next to that.