In Windows 8 or 8.1, PC Settings may not start: clicking on it very briefly shows the purple background but then returns to the desktop or start screen. The Application event log shows the following error (or a similar one):

Event log
Activation of app windows.immersivecontrolpanel_cw5n1h2txyewy!microsoft.windows.immersivecontrolpanel failed with error: This app does not support the contract specified or is not installed. See the Microsoft-Windows-TWinUI/Operational log for additional information.

A possible solution is to re-register the PC Settings app (also known as Immersive Control Panel) through Powershell. Run the following from an elevated command prompt:

powershell -Execu  ...