the 2002 Ford Explorer shift selector for the transmission operate by computer

Shifter does not move? ... Gear selection cannot be made? ... Vehicle does not move?

The mechanical part works fine. It seems like the computer isn't reading something

The shifter itself works fine.

Intermittently does not work. I can select a gear and it operates good, then sometimes I select a gear and it does nothing

Unfortunately - intermittent concerns are very difficult to pin point - without proper diagnostic testing equipment connected at the time the failure is present - and operated by qualified personnel - there is very little chance the problem will be discovered. Good luck with it.