1
Open the old Control Panel (not the settings app)
At the top of the old Control Panel, set view to icons
Open Power Options
On the left, click 'Choose what the power buttons do'
At the top right, click 'Change settings that are currently unavailable'
Under 'Shutdown settings' disable this setting - 'Turn on fast startup'
Save that and close Control Panel
Restart (not shut down) your PC to apply the change and flush out your RAM.
Then check if that resolves the problem.
2
If that does not resolve the problem, on your Desktop, press Alt + F4, are you able to use the resulting dialog box to shut your PC down.
3
If that does not resolve the problem, go to the support page for your PC on the manufacturers website to check for any BIOS update that may be available and not yet installed.