I tried Command D and it just restarted my computer and loaded everything up. I tried Option D and got the same thing with regular D.
My computer has been running very slowly for awhile now. I have quite a bit of
hard drive storage (I am only using 453G out or 500 G.) I haven't added any ram but why should I? I don't plays games and only surf and do email mostly. I used OnyX to clean stuff up but it doesn't help speed things up. I haven't added any new plug-ins in quite awhile. I'm stumped. So, I thought maybe my hard drive was going.
Oops! I meant to say option-D.
Your symptoms don't sound like your HD is going, but it won't hurt to run AHT.
Can you post an iPhone pic of the "D"/option-D screen that's got you stymied so we can see what's happening? There's no apparent reason why you shouldn't be able to boot into AHT.