If you mount any disk on the root partition, the contents will take precedance and you will be unable to access any files in the "real" root partition.
Note that root is a, er... really important part of your filesystem. You can't do anything without it!
You should always mount extra devices on /mnt (traditional mount point) or perhaps /media as is now becomming popular. You could add other mount points within these directories if you want.
Unmount your extra storage to get access to root again and add it as above.