just installed mountain lion on my iMac early 2008 (downloaded from App Store)
I'm trying to run apple hardware test by pressing "D" or "ALT + D" but nothing happens...
Solved by baltwo on Nov 16, 2012 11:52 PM
You can't. Call AppleCare and request replacement discs. They're available for a nominal S&H charge.
Reply by Linc Davis on Nov 16, 2012 9:21 AM
To activate the Apple Hardware test you must restart your iMac and hold Option key + "D" before the Apple Chimes. That only works on a Mac that's capable of Internet Recovery, which a 2008 iMac is not.
Reply by baltwo on Nov 16, 2012 7:55 PM
Appears you got bit by ML which seems to blow away the AHT. See my solution at https://discussions.apple.com/message/20014699#20014699 on how to restore it and get CMD+D to work on your machine.