How to stop Terminal from opening instead of Finder functions, such as New Folder, Open File, copy, paste, trying to move a folder to Desktop? When trying to open new folder on Desktop from Finder-menu Terminal opens instead. Also I cannot move documents and folders onto Desktop- get a "forbidden" sign (= white circle with slash through it).
When accessing the computer as other user Finder works fine.
Was running Mac OS 10.7.5 and it did not help to upgrade to El Capitan which I downloaded a few days ago.
After repairing permissions the report stated 


  Warning: SUID file “System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/MacOS/ARDAgent” has been modified and will not be repaired. 


Disk Utility says the disk is OK. 

I have tried to remove my user-systempreference-plists for Desktop and Finder, but everything got worse (spotlight could not find the right files, etc.) so I put back the plists.

Is this a sign of a "damaged directory"? Can it be fixed by Disk Warrior? Please help!
Found a solution to the problem here:


  Enter the following command in the Terminal window in the same way as before (no typing):

xattr -c ~/Desktop

  
  Try the action again. If the same thing happens, relaunch the Finder by selecting Apple menu > Force Quit... > Finder and pressing return or clicking Relaunch.