Finally get Apple Hardware Test running

I read some blogs and found that there exist something called Apple Hardware Test.  Since I sort of figured out that a memory chip on my MacMini had problem, I was thinking that it maybe good to ultimately find out which memory has problem.  And this tool seemed like a prefect way to do so.

 So I held down keyboard button D before restart the Mac Mini.  I tried option D, still didn't work.  After a LOT of fustration, I eventually found out that option D doesn't work on my MacMini late 2009, while my model requires loading up the disc "Mac Mini, Application Install DVD" disc (NOT the MacMini Mac OSX Install DVD, nor a OSX Yosemite flash drive that I created)  That's a problem since my internal DVD drive failed.  Eventually I found out that the external USB DVD Drive worked, but I need to unplug all network cable and other USB harddisk conenction.  (I also REMOVED all partitions in my internal harddisk, which I would do it regardless since there seemed to be some drive access issue anyway.  Don't know if it's related to being able to boot up Apple Hardware Test eventually.)  With that, I only have power cable, monitor cable, and USB cable connecting to my USB external DVD drive.  

That worked.

(Someone also suggested downloading Apple Hardware Test dmg and burned it on a Flash drive.  My approach worked for me so I didn't try that one.)

So I ran a test on my current setting: 4Gb Ram Module at bottom slot, 1Gb RAM Module at upper slot.  And I found no memory error at all.  I got a SATA error, though.  But then I searched the web found out that it's probably a false alarm. So I kind of ignored it.

When I swapped in another 4Gb Ram Module and ran the test again, I got the following error:

Alert! Apple Hardware Test has detected an error,

4MEM/9/40000000:0xa89ae618

So now it's proven that there IS indeed error with the memory.  Since it supposed to come with lifetime warranty, I am going to send it in and got it replaced.