I have a late 2012 Mac Mini with Mountain Lion installed. I have had the Mini for around 6 weeks and am using as a media server.
When the Mini goes to sleep (either automatically or by manually telling it to) it refuses to wake up. The power light is pulsing.
The Mini is connected via HDMI to a home cinema receiver (which is in turn connected to a TV) and has an external USB hard disc and USB hub attached. There is a wireless keyboard and mouse attached via USB also.
In the Energy Saving preferences I have all tick boxes enabled apart from "put hard discs to sleep". I have tried the wireless keyboard, mouse and the Apple Remote app to wake the Mini to no avail.
Any ideas? I really need it to sleep and wake when needed as thats an essential feature of a media server.