We have one windows Server 2008 R2 installation and we need the power button to trigger the server's shutdown procedure.
Generally this works as expected, but when there's a blocked session the shutdown does not happen.
I have googled this requirement wide and far, but I have been unable to find anything related.
You could use the Windows Task Scheduler to create a task triggered by the power button event (I'm not sure about the EventID, perhaps 109 or 1074).
The task will call the shutdown command:
shutdown /s /d p:0:0
/s shutdown command to the local computer/d this records the reason for the shut down (p is planned and 0:0 indicates an "Other" reason)