I am having the same issue with D34010WYK.
The power button used to work ok at first. I have Linux Mint 17 and XBMC installed and was quite happy with the box. The only thing I missed was setting it into sleep mode, it just hung instead. So I made quite a few experiments using info from various forums and trying to make it go to sleep. Each time the box crashed and required a hard reset with a power button. And the same power button could be used to start it again.
The final experiment was item 1.3 from http://wiki.xbmc.org/index.php?title=HOW-TO:Suspend_and_wake_in_Ubuntu. So I added "usbcore.autosuspend=-1" to GRUB settings rebooted and tried to send the box into sleeping mode again. It crashed as usual but the power button cannot be used to start it back anymore.
I have the latest BIOS version 26, WOL can still be used to start the box but not the power button. I tried to reset BIOS settings to default with F9 but it did not help.
Hope my information would be helpful.
TON