Does the machine display any errors or requestors before dropping you at the command prompt? Typically, I'd expect it to look like:
AMIGA ROM Operating System and Libraries
Copyright 1985-whatever
All Rights Reserved.
1>
Does yours look like this, or have other stuff?
What does typing the following command print....
sys:c/cd
and does
sys:c/dir
call up a listing that shows directories like C, S, Libs, Prefs, Utilities, etc....?
Maybe your computer is trying to boot from something other than the partition you installed Workbench to?