iPhoto - When I add new photos to iPhoto from my iMac they do not appear in the "Photos" library. They do appear in Last Import. Any thoughts?

If you are seeing your photos in "Last Import", the photos are somewhere in your library. Perhaps the dates are wrong, and you do not see the photos arranged by date, where you expect them to be.

Select one of the photos on "Last Import", then ctrl-click it and select "Show in Event". That will take you to the event in event view.