RE: Linux Mint KDE 9. I inactivated the desktop because of unwanted items, hoping to get back to the original desktop, and now when I log in I see a black screen with no option to use the cursor. Logging in as root or another user displays the original desktop.

How can I restore the original desktop?

If I understand you correctly, doing the following from a shell should suffice (with KDE, or at least plasma, not running):

mv /home/user/.kde/config/plasma* /home/user

Log in again and you should get whatever default Linux Mint is using.

re: mv /home/user/.kde/config/plasma* /home/user

I started the OS in recovery mode, and at kde ~# typed the above with 'user' replaced appropriately. The response is "Cannot stat [the above command], no such file or directory."

Did I type the command correctly? In /home/user there is no such directory.

I appreciate your help.

Okay, it might be .kde4 instead of .kde. It depends on the distro which one's used.

It would seem to me that the issue may be that plasma desktop isn't starting when KDE starts.
Something else you can try is when you get to the login screen change the session to something other than KDE (like failsafe which will open a blank session with just an xterm window - use ctrl+alt+backspace to exit), and from there launch plasma-desktop to see if it comes up. If it does come up with the desktop as expected then for some reason it is being excluded from the KDE session (I'm not sure off-hand how to fix that). If it doesn't come up then it is possibly a bad config, in which case try removing the ~/.kde(4)/share/config/plasma* files and try again.