How can I enable the power button on my server?
You just need to install acpid package (sudo apt-get install acpid), its just one package, nothing more and it will handle all powerbutton events (acpi-support contains more additional packages). Tested on ubuntu server 11.10
https://lists.ubuntu.com/archives/ubuntu-users/2011-November/253766.html
I believe you might need acpi-support. Check out the links below for more info on how to manipulate the power button press event.
http://blog.metalight.dk/2010/07/ubuntu-lucid-custom-power-button-event/
http://test.z13media.com/2010/03/disable-power-button-on-ubuntu-server.html