Sounds like your savegame is partially corrupted.
I hope you have a backup or another recent savegame.
Normally when you change a class to a Jedi class, you can expand the Jedi class node and find a child node named "Force Powers". Highlighting that node should bring up a selection list where you can add new powers. Sounds like the corruption occurred back from the very first step where it didn't let you add new powers. :-?