1
If the power options on the start menu are not available, if you right click your Start button, are those options available on the right click menu in the Shit Down or Sign Out' section.
2
If not, on your Desktop press Alt + F4, does that bring up the shut down dialog and are you able to use that menu to shut down or restart your PC.
3
If neither of those options work, have you installed a browser named the Lockdown Browser to take an online exam?
4
Also, click your Start Button, type regedit and hit Enter to open the Registry Editor.
Click View and make sure 'Address Bar' is turned on.
Paste this into the Address Bar at the top and hit Enter.
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
In the right hand pane, is there an entry named NoClose
If that entry exists, right click it and delete it.
Then close the registry and force your PC to shut down to apply the change, then check if the power options are available on your Start Menu.