How can I disable the windows button on the keyboard while my application is focused?

I'm having an endless problem with users accidentally pressing the windows key on the keyboard which causes the application to lose focus. They are capturing data, so when they finally realize that while they were typing nothing happened. They have to find the place where they lost focus and redo everything from there. This is very time consuming and as we are paying our data capturers by the hour this turns out to be an expensive flaw in the application.

Can anyone please help me?