recreate the users configuration folder as outlined in step 12 of the Adobe troubleshooting guide:
after renaming the configuration folder, start DW to recreate it, then close DW.
Open the extension manager, and uninstall the extensions, then install them again.
After installing them in the extension manager, open DW, this should start the WebAssist installer, if it does not open automatically, open a php page to force it to start.
After the WebAssist installer completes, restart DW.