Comment 9 for bug 40243

Jarlath,
I would suggest that you do the following:
Check your bios settings. There will likely be a setting which sets the functionality of the power button. Try some different settings here. The usual options are Suspend to RAM or Disk, and "hold for 4 secs for hard power down", "signal to OS for soft power down" (there maybe more options than this).
It maybe that that you are experiencing some sort of bug with regards to ACPI support for your motherboard.
Try the debugging procedures here:
https://wiki.ubuntu.com/DebuggingACPI

If none of the above helps then file a new bug report. File it against the Linux-source-2.6.xx (depending upon which release you are using).
Please include the information as separate attachments:
 * Output of uname -a
 * Output of sudo lspci -vvnn
 * Output of sudo dmidecode
 * Try to suspend/hibernate and then restart the system and attach /var/log/kern.log.0
 * Tarball of /proc/acpi directory. You can't just tar all files because their content sometimes changes etc.
    * cp -r /proc/acpi /tmp
    * tar -cvjf ~/acpi.tar.bz /tmp/acpi
Thanks.