Can't boot Apple Hardware Test with correct install disk that has AHT I just restored my HD from a Time Machine backup and afterward my AHT won't work, despite the fact that I have the original install disk (10.5 Leopard, disk #2 that says it has AHT on it). AHT worked a week ago, no problem. I'm 100% sure I have the right disk. I've successfully run AHT many times using this disk in the past. 

Weirdly, I can still boot to Recovery Mode from the same disk by hitting Command + R (unfortunately, can't reach AHT that way). I ran First Aid from disk just in case, no problems found. So the disk drive, disk, and keyboard all seem to work okay.

I shut down, hit D right after hitting the power button, and screen goes gray forever, never boots. Same thing occurs when pressing Option at boot to choose the boot disk... goes to gray screen, never boots. I'm using a wired USB keyboard (a Microsoft brand, but I'm accounting for default option key vs. command key vs. windows key, etc.). I also tried hitting D at different times after hitting power, before hitting power, and tried different USB ports for the keyboard. Unplugged everything. All fails. 

I assume my HD recovery changed something. Apple support said they think my disk is bad, which I don't buy since it worked last week.  

Perhaps relevant: I want to use AHT because — before I recovered my HD — AHT indicated I had bad ram. (Ram problems were intermittent). I wanted to determine which of my two chips was bad by using just one or the other and repeatedly running AHT to find which individual chip is bad. Currently using just one of my two 4GB chips, which I guess could be related, if it's the bad one. MacMini is a 3,1 Intel currently running 10.11.6 btw. 

Thanks a lot for any advice.
My first thought was that perhaps you had somehow updated the firmware and were trying to use an AHT disk that couldn't boot due to this. This is a possibility because your Mac Mini came pre-shipped with Mac OS X 10.5.6, but the firmware update (which you do have installed) requires Mac OS X 10.5.7. However, then I realised your question says you only just ran the AHT last week. So, unless you somehow updated the firmware in the past week, this isn't likely to be your problem.

Since you can't seem to get your disk to work, the only other option I can think of is to download AHT again and run it from a USB. The steps to do this are as follows:


Create a bootable USB flash drive by using Disk Utility's Erase function. Make sure you choose OS X Extended for the format and the GUID Partition Map for the scheme. For the purposes of these steps, also give your USB the name AHT when you're erasing it.
Download the AHT for your particular Mac Mini here
Mount the downloaded image (it should mount as AHTCThree)
Now you will need to copy the AHT to your USB flash drive. To start, Launch the Terminal app (usually found within the Utilities folder)
In the Terminal window, enter the following:

cp -r /Volumes/AHTCThree/System /Volumes/AHT/
Now we need to make the USB flash drive bootable, so enter the following line in Terminal:

sudo bless --folder /Volumes/AHT/ --file /Volumes/AHT/System/Library/CoreServices/.diagnostics/diags.efi --label AHT
Enter your Admin password
Leave the USB flash drive plugged in and restart the Mac Mini
Immediately hold down the Option key
Select the AHT from the list and boot up


NOTE for other readers: - These Terminal commands were written for this specific question. However, these can be adapted for your use by replacing the AHTCThree with whatever name your downloaded disk image mounted as at Step 3. For example, if at step 3 your downloaded disk image mounted as AHTEOne, then at Step 5 you would use AHTEOne instead of AHTCThree within the Terminal command.