While moving HD icon I placed it on top of or near the xcode icon on desktop. now xcode won't run. All hardware tested fine at apple and we reinstalled operating system. also HD icon removed from desk. Activity monitor %150 from xcode. Xcode removed and reinstalled twice. Girl at Genius bar stumped too.
Mac Air OsX 10.8.2
@xnav : perfect description of the problem, and your solution solved the issue on my side
I had this happen when I accidently told Xcode too open the directory that contains all my projects. If Xcode works from a new/different user ID then try deleting everything that starts:
~/Library/Preferences/com.apple.dt.* under the user experiencing the problem.