Why is Apple hardware test (AHT) not loading when pressing key D on system start? I purchased a Late-2011 MacBook Pro 15" used a month ago. At the time of purchase, I successfully ran the Apple Hardware Test.

I've since installed a new SSD and aftermarket RAM. The computer appears to be functioning normally (I'm typing this post on it), but I'd like to run the full hardware test to verify everything is OK.

But I can't seem to get it to load into the hardware test.  I've tried holding down D before pressing the power button on as well as right before the grey screen comes up. I'm confused because I've done this before without any problems.

Is there something obvious I'm doing wrong or is there a way I can check for problems that would stop the AHT from starting?



Additional info by @gentmatt:

The last time I have performed the Apple Hardware Test, my MacBook Pro was running 10.7.2. As of today, I'm running 10.7.3.

The AHT loaded even after I had installed my custom SSD and RAM. But not this time.
Pressing &#x2325;+D right after pressing the power button and before the gray screen appears works on my late-2011 15" MBP. This forces an internet-based hardware test, which will work even if you've lost the the local hardware test software. (It will probably work over WiFi, but you have more chance of success with ethernet.)