KDE power management system could not be initialized

First of all, apologies but I am very new to using kubuntu, so I would need a very basic step by step answer to solve this problem. Since my last update I am getting this error message:

KDE power management system could not be initialized.

When I go into 'power management' it says:

Power management configuration module could not be loaded. The power management service appears not to be running. This can be solved by starting or scheduling it inside 'startup and shutdown'

I followed the steps that I found mentioned by others online.

Go into System Settings --> Startup and Shutdown --> Service Manager (tab) --> Startup Service and tick the 'Power Management' box.

However, this was already ticked and also I have a desktop computer so don't know if this is actually needed. I tried unchecking it to see if it makes a difference but it does not.

I am very confused as to what should be done to solve this as now I don't have the option to shutdown the computer or put it into sleep mode. Any advice would be very much appreciated. Thank you.

I had the same issue (and WiFi was not working). Reinstalling of upower solved it:

sudo apt-get purge upower
sudo apt-get install upower

In the application launcher menu the entries for Sleep, Shut Down and Restart were missing! Also the WIFI didn't work.

I reinstalled (or just reinitialized) upower:

sudo apt-get install upower