Is your main HD your boot drive? If not, it could be that directories in /Volumes have become mixed up in a crash. By default, OS X makes new directories for all non-boot drives, using the name of said drive, in /Volumes and deletes them as required - e.g "/Volumes/My HDD" for a drive called My HDD. If there is already a directory with that name in /Volumes, it does not reuse that directory, but instead adds a new one called "My HDD 1" or (maybe 2, I don't remember). Presumably sidebar tries to connect things up to hide this.