Miscellaneous topics that do not fit into specific categories.
You are correct the LockDown browser is know to cause this problem.
1
If you still need to have that browser installed, on your Desktop, if you press Alt + F4, does that open the Shut Down dialog on your Desktop to allow you to shut the PC down?
2
If you no longer need the Lockdown browser installed, uninstall it, force your PC to restart and check if that resolves the problem, if not, please let me know and I will provide you with a solution to restore the settings that browser removed form Windows.