You can prevent your users from shutting down the server via registry or GPO here :
To get started, open the Registry Editor by hitting Start and typing “regedit.” Press Enter to open Registry Editor and give it permission to make changes to your PC. In the Registry Editor, use the left sidebar to navigate to the following key:
Set the value to 0 in the “Value data” box and then click OK.
It is also possible through group policy to allow only administrators to perform a shutdown.
Click execute, and type in gpedit.msc
Locate and edit the following GPO :
Computer configuration / Windows settings / Security Settings / Local Policies / User rights Assignment / Shut down the system
Remove the Users group and domain users to leave only the administrators. This setting may need a reboot to take
If you’re using Windows 10 Pro or Enterprise, the easiest way to hide the shutdown button on the login screen is by using the Local Group Policy Editor.
In Windows 10 Pro or Enterprise, hit Start, type gpedit.msc, and press Enter. In the Local Group Policy Editor, in the left-hand pane, drill down to Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options. On the right, find the “Shutdown: Allow system to be shut down without having to log on” item and double-click it
On the Local Security Setting tab, click Disabled and then click OK.
Exit the Local Group Policy Editor and restart your computer to test the changes. If at any time you want to show the shutdown button on the login screen again, just follow the same procedure and set the “Shutdown: Allow system to be shut down without having to log on” item back to Enabled.