reset the workspace layout:
go to Window -> Work Space layout -> Reset '<your layout name>'
and Delete the Dreamweaver Cache file from the users configuration folder:
http://www.webassist.com/tutorials/Common-installation-issues
if you continue to have a problem, please provide more details:
What is your OS?
What version of DW?
What extensions including the version numbers are installed?
What are the steps you are taking to reproduce the error?