ok, it could be one of several things - if you crashed out of the file, or the program shut down unexpectedly, check and see if you can open one of the backups. They'll be in the same folder as the project rvt file. If you can open the backup, save yourself a lot of time and work from that version.
Check the properties of the file, and make sure it's not set to ready only.
Windows Desktop is just folder under your user profile, so if any of your profile settings got changed, it could populate back down to the file. You can try moving the file to another location and see if it will open. I rarely store project files under any of the user folders or My Documents locations. Better to create a local projects folder in this case, like c:\projects, and storing project files there. That way, if your user profile gets corrupted, you don't lose anything if it has to be rebuilt.
Try the backup file first and let me know if it opens.
thanks - db
David A. Butts
Virtual Design and Construction Manager - Kimley-Horn
Revit Certified Professional/Autodesk Certified Instructor
Revit, AutoCAD Architecture, MEP, Plant 3D, BIM Collaborate Pro Subject Matter Expert
The MEP BIM/CAD Engineer Blog
