This is for in iMac G5 running OS x 10.4. It is a customer iMac.
Apple Documentation says holding D key down during startup causes the the Apple Hardware Test (AHT) to run for intel baed MAcs (and I assume for Power PO based Macs too). Apple documentation ALSO says that for 10.4 the AHT is on the Install CD so I put the 10.4 install CD in the CD drive and restarted with the D key held down, got a single tone and THE AHT NEVER APPEARED. Instead a blue bar moved left to right and beneath it, it said Starting MAC OS SX and it never got beyond that screen. I have tried holding the D key down for a long time after restart or a short time and I get the same result. I know the key board is being recognized because holding the eject key on the keyboard at boot causes the CD to be ejected. Also holding the option key down at boot let me to a screen with OS X HD showing in a rectangle which is correct if there is only one OS (OS X) on the HD
What am I doing wrong. How can I get AHT to run?
You may ask why do I want to run AHT. Because at first normal boot it made a noise that sounded like a fan; it was not a clicking noise like a bad HD. All later normal boots result in no noise and it goes to OS x startup screen and hangs there.
Customer reported noise at normal startup too.