IMac – How to download something with display turned off (Ctrl+Shift+Eject)

Realised I answered a dupe of this here: How can I download something with display turned off (Ctrl+Shift+Eject)?

My answer to that question below:

I always use this combo as well, however this does not immediately sleep my machine in ML.

I believe this is a separate issue at play here. According to Siracusa's ML review, unlike in previous OS X versions, in 10.8 your system is eligible for sleep immediately upon "user inactivity" (the inactivity delay being set in your energy saver settings) unless the currently running apps make "power assertions".

In this case, that key combo is signalling to the OS that "user inactivity" should be triggered right away. In such a case, if your particular app that's downloading stuff does not make power assertions, your system will sleep.

I have come across the same issue generally (not necessarily related to triggering the screen sleep combo). See: Mountain Lion sleeps too aggressively

To fix the problem you should try to see if the problem is hardware or software.

We are going to rule out software because of the hardware testing that was completed.

As noted in OP's comment

... But I tried connecting the wireless keyboard to my MacBook, and the Eject key did not work there too ...

Since this problem persisted across multiple macs that strongly points to a hardware issue with the eject key on that Apple wireless keyboard.

If your Mac that the keyboard came with still has some coverage under AppleCare then Apple should cover repairing or replacing the keyboard according to AppleCare - Mac and Apple Display Coverage

What’s covered — Mac

• Your Mac computer

• Included accessories such as the power adapter