Hello! Every so often after a reboot, the KDE power management daemon decides to not work properly. This causes the power button to not act as I expect, no automatic sleep, and screen/keyboard brightness to quit working. After digging around the internet and playing around with my computer a bit, I found the solution is to restart the power management daemon.
Kill the power management daemon via terminal command
Start powerdevil again.
Note: The binary is installed to /usr/lib not /usr/bin
Put your computer to sleep USING THE SLEEP MENU important then wake it up (this helps re-register power buttons if you have configured them to do something other than shut down the computer)
Enjoy having your problems disappear