I have been loving my 27" iMac. Today I finally got a Thunderbolt cord so I could start using it in external display mode with my work 15" rMBP. Everything worked fine for awhile -- so I turned it off and went about doing other things. A few hours later I tried again to put it into target display mode (Command F2) and it didn't respond. Re-started both machines, still nothing. I went into the System Profiler and under Thunderbolt on the iMac it says: Thunderbolt: No hardware was found On the MBP, it reports that there is a Thunderbolt Bus and the details. This leads me to believe that somehow the Thunderbolt card in the iMac has failed. Any other ideas?