I just got my Xbox 360 Slim back from Microsoft, and when I initially tried to turn it on one day via the Eject button it would not turn on, but it would make the "bing" sound as if the tray was ejecting, then shortly after my Xbox started freezing on bootup, and thus had to send it in.
Now, when I connect the Xbox 360 Slim to the power brick, it will turn on from the controller or the power button right away, but I'll have to wait 15 seconds or so if I want to turn it on via the Eject button RIGHT AFTER plugging it into the power brick, but if I turn it on via the power button then turn it off, it will turn on via the eject button right away.
So, once everything is hooked up from NOT being hooked up, the eject button just makes the BING sound without turning the Xbox on, but 15 seconds later then it will turn the Xbox on. However, the power button and controller both turn it on right away. And if I turn it back off, the Eject button will turn it on right away.
Anyone have similar experience with this? Can you try unplugging the Xbox from the power brick, plug it back in, and tell me if the Eject button turns on the Xbox 360 Slim? This is what it did before it totally locked up, so I'm hoping it doesn't happen again, even though it DID freeze when downloading YouTube App.