[2008] Secondary Logon Form

Just for fun, I was trying to make an application to put on my computer at startup that will ask for a different password than my normal one to log in. If it's wrong after 3 times, they're logged off of the computer.
The problem is making the program un-closeable and full screen...disabling alt+tab.
Anything that would allow the user to somehow minimise or otherwise ignore my second login screen.
I would really like this to force the user to input the password, or they can't do anything at all.

Code:

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System.Diagnostics.Process.Start("shutdown", "-l")

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Is the code I have for logging off the user.
Could anyone get me on the right path to accomplishing this?