CAD tip # 7475:

Always backup any customized files before deleting any information

1. Under the user account you want to reset start the Registry Editor - regedit (Windows > Run)
2. Browse to the key:
   HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R18.x\ACAD-xx00:40x
   (depends on version, language and vertical) and delete it
3. Exit the Registry Editor
4. Delete the following Windows folders (please note that some folders may be set as "hidden"):

   WinXP:
   C:\Documents and Settings\USERNAME\Application Data\Autodesk\AutoCAD 2011
   C:\Documents and Settings\USERNAME\Local Settings\Application Data\Autodesk\AutoCAD 2011

   Win7/Vista:
   C:\Users\USERNAME\AppData\Roaming\Autodesk\AutoCAD 2011
   C:\Users\USERNAME\AppData\Local\Autodesk\AutoCAD 2011

   E.g. for Civil 3D 2011 use "C3D 2011" instead of "AutoCAD 2011" for the last subfolder.

5. Start AutoCAD to launch the secondary installer - this will restore the default user settings (subsequent starts are then performed normally)