C:\WINDOWS\system32\config\systemprofile\Desktop is not accessible?

This is caused by the desktop reverting to a mandatory login profile, being caused by a new file in your user directory labelled ntuser.man, and has happened to me twice while doing Windows updates. Simply rename this file to something else and login. The trick is getting access to this file to rename it. The best way is to do it is from another administrator account.

The file is:

c:\users\<profilename>\ntuser.man

Change it to:

c:\users\<profilename>\ntuser.m.a.n.safe    (or anything else)