PROBLEM:
The Project Browser and Properties dialog boxes become unresponsive. You are unable to move them and nothing happens when you clicking in them.
Usually happens after Revit crashes.
CAUSE:
Revit bug in 2014 and 2015.
SOLUTION:
Edit windows registry (WARNING changing things in window's registry can be dangerous)
Run regedit.exe (type regedit in start search box)
Open
HKEY_CURRENT_USER
>Software
>Autodesk
>Revit
Rename folder (right click and pick rename)
Autodesk Revit 2015
to
Autodesk Revit 2015_backup2