Hello, I bought a second hand Mac Pro this summer, but had to send it back to the seller, due to an error showing up in the Apple Hardware Test. (I have one year warranty) Now I received the Mac back and I wanted to run the test, just to see if it's all okay, and it doesn't seem to work. The seller has changed the hard drive with a different version of Mavericks, because something with my Mavericks was weird apparently (I've installed it from a USB drive). I've tried starting the test by holding the D key, then Alt + D, but nothing happens, I land on the desktop each time. Does anyone have an idea? Thanks a lot.