Sounds like the web assist installer has not run to finish the installation.
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:
then with DW closed, open the extension manager. in the extension manger, uninstall the extensions, then install them again.
When you open DW< it should launch the Webassist installer, if the WA Installer does not open, open a php page to force it to start.
After the WA Installer completes, make sure to restart DW.