How have you tried?  Application Launcher/Leave?  Command line sudo halt?  Any error messages?  Do any other things work, like trying to simply log or or to reboot?  Do you boot straight into KDE or command line?  What else has recently changed?  I don't know if it matters, but what kernel, and what version of KDE?

I understand the pain, but this is not the proper channel for this issue. This bug was opened against khelpcenter, an browser for help guides, which is for sure not the right component. But this is not even about software by the KDE community, or at least not directly. If the desktop environment used is KDE Plasma, this may be relevant here, but I would first check on the proper support channel for Debian, providing more details.

Created attachment 102136 [details]
attachment-8777-0.html

My knowledge of Linux is very limited , I have installed Debian 8.6.0 from
a bought disc , & log in with a password as usual . It is the shut down
function as used from the menu that does not work . At the moment I have
taken the hard drive with Debian on it out of the machine & have gone back
to using Linux Mint .

On Sun, Nov 6, 2016 at 11:17 PM, Luigi Toscano <bugzilla_noreply@kde.org>
wrote:

> https://bugs.kde.org/show_bug.cgi?id=372139
>
> Luigi Toscano <luigi.toscano@tiscali.it> changed:
>
>            What    |Removed                     |Added
> ------------------------------------------------------------
> ----------------
>              Status|UNCONFIRMED                 |RESOLVED
>                  CC|                            |luigi.toscano@tiscali.it
>          Resolution|---                         |INVALID
>
> --- Comment #2 from Luigi Toscano <luigi.toscano@tiscali.it> ---
> I understand the pain, but this is not the proper channel for this issue.
> This
> bug was opened against khelpcenter, an browser for help guides, which is
> for
> sure not the right component. But this is not even about software by the
> KDE
> community, or at least not directly. If the desktop environment used is KDE
> Plasma, this may be relevant here, but I would first check on the proper
> support channel for Debian, providing more details.
>
> --
> You are receiving this mail because:
> You reported the bug.
>

(In reply to John from comment #3)
> Created attachment 102136 [details]
> attachment-8777-0.html
> 
> My knowledge of Linux is very limited , I have installed Debian 8.6.0 from
> a bought disc , & log in with a password as usual . It is the shut down
> function as used from the menu that does not work . At the moment I have
> taken the hard drive with Debian on it out of the machine & have gone back
> to using Linux Mint .

A reason more to ask on Debian-specific channels. I marked the bug as INVALID only because this specific bug tracking system is not the proper place to report it.