Quitting System Settings

I get an alert to agree to ICloud terms. I usually cancel as I do not want to store data in the ICloud on my MacPro laptop. Now I cannot get the window to allow me to use the cancel button that I would agree to the new ICloud terms as I have been doing. This has resulted in me not being able to close my system settings window. I can do check my email and go online, but I cannot close the agreement window or the System Settings window. When I try I get the "boink" sound and nothing happens. I cannot even click on the box for agreeing, there is no sound, but the box does not show a check sign.

What do I do to close my system settings window?