Ah, I wish it was that simple. I've installed Alchohol which adds a virtual drive which is what messed up the device letters. Not so easy to unplug or reassign.
I don't know what "Alcohol" is (in this context!!!), but if it assigns a drive letter, you should still be able to change that letter to a different, currently unused letter. I believe that in the Disk Management section you can lock a letter to a particular drive so that it won't get changed if you add other drives. I know I have done this in the past so that my DVD drives don't change letters when I add a new external drive (I'm now up to "Q:" ).