So I'm trying to run the Apple Hardware Test. I start the computer up and hold "D". It boots into OS X like a normal startup. So, I plug in the Ethernet and hold option-D to do the AHT from the Internet. It tells me "Apple Hardware Test does not support this machine".
So, I try to install the "iMac EFI Update 1.8" from http://support.apple.com/kb/DL1493 (which is for my iMac model, which is a iMac (Mid 2010)), but it says "This software is not supported on your system." I also tried the later version, v1.9, from http://support.apple.com/kb/DL1498 but it isn't for my iMac and so I get the same error.
I also tried putting in my DVD 1 for my iMac, then starting up by holding both "D" and "option-D", but neither booted AHT from the DVD.
So now I'm stuck. What should I do now?