When Revit has a case of the Mondays, that is, none all of the windows (properties, project browser, etc.) seem to be frozen and you're treated to repeated blasts of whatever noise your computer likes to make to let you know to 'stop clicking that,' you can spend tens of minutes trying to break it free.
Fortunately, there is a Konami code to fix this - just start a new project and save it as a file on your desktop. This seems to snap any version of Revit out of its stupor. The Big Blue R saves the day!