Apple's article on running Apple Hardware Test says nothing about an encrypted startup volume.
iMac, OS X Mountain Lion (10.8.1)
BTW, this is a mid-2007 iMac 24" extreme. So it can't be upgraded to load diagnostics over the net.
Turn off encryption and try again. If no go, boot with the AHT disc that shipped with the machine and use that.
I hope no-one does turn off their hard disk encryption when they suspect that the machine is broken. This will very likely destroy the data on the hard drive.
-Pete
For that case, one should always have an unencrypted bootable backup/clone of that which they're encrypting.
The D startup key doesn't work on an encrypted drive on Mountain Lion. How do I run the diagnostics?
