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 problems, please provide more specific details about the steps you are taking up to encountering the problem, and also system details:
What is your OS?
What is your DW Version?
What Extensions, including the version numbers are installed?