Ford Mondeo not starting

I stopped to pick up a friend and the car would not start again ,plenty of diesel in it ,had to get aa relay home .The injectors were checked ,one was replaced ,and I bought a camshaft position sensor as I was told this maybe where the fault lies,but I don't know we're it is in the engine bay ,it seems as if its an easy job ,I would be grateful for any help in locating the sensors position Thanks