locate the users configuration folder, this is the folder that contains the DW Cache file, and rename it.
open DW to recreate the folder , then close it again
open the extension manager, is the extension manager, remove the extensions, then reinstall them.
make sure to download the latest version available from the download center.
After installing the extensions in the extension manager, when you open DW, it should launch the webAssist installer to complete the installation.
If the WA Installer does not open automatically, open a php file to force it to run. make sure to restart DW after the WA Installer completes.