@dayne > Sounds like you broke your database! It may have been that rekordbox hadn't fully terminated before you shut down, or there was some other process which was interrupted.
To remedy the situation, the best bet will be to start from scratch and start re-importing everything (as it sounds like it was all newly imported anyhow).
With rekordbox closed, open your Explorer and go here:
C:\Users\<yourusername>\AppData\Roaming\Pioneer\rekordbox
Rename datafile.edb to datafile.edb.old
Restart rekordbox and it should be blank and working. Try importing a folder or two worth of tracks to see if that goes well.