There has been an issue reported where using multiple dropdown menus within AutoCAD 2013/2014 with Windows 8 will cause the program to freeze. Ending the process in task manager has been the only way to close the program. It appears as though the cause has been found. Evidently if you have a iPhone plugged in to your computer while running AutoCAD, this freeze can happen. Unplugging the phone causes AutoCAD to work correctly again.