Disable hot keys with C# code

I have a c# application in (xaml) that runs when users log into a windows machine. The app is a popup form that maximizes and asks the user to click a button to continue. The behavior I want if for the user to NOT be able to do anything else until they click that button. Right now, users can bypass it by hitting the windows key, bringing up task manager and ending the app. If they start another app, it will start but they cannot see it as it is behind my form. They can also alt-tab out of it. Is there a way to basically freeze the use out of doing anything else until they click that button? Thanks for any help.