The Editor uses a configuration file located in the %USERPROFILE%\Application Data\F5 Networks\iRuler directory titled iRuler.xml. This contains all the keywords for autocompletion. First thing I'd do is look and see if this file is there. If not, you can regenerate it in the editor with the "Tools.Reset Config" command. This will save a default config file to that location. If, after you do that, it still isn't present on disk, then odds are you have a permission problem in not allowing the file to be written to disk.
If the iRuler.xml file is on disk and you still don't have auto-complete working, let me know and I'll try to get you a debug build to diagnose what's causing the problem.
-Joe