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 Shut 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 Respondus Lockdown Browser to take an online exam?
4
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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer
Please provide a screenshot of that Registry Editor page.