Run ZQ. Press X for preview. If you press a function and either the PageUp or PageDown keys simultaneously, keyboard functions cease to work and so will be the mouse because you can't do anything with it. You are stuck, the program is not frozen but the last thing to do is to force ZQ to close using Windows Task Manager.
(Note that timed saves DO NOT work in preview mode, you MUST force to shut down ZQ.)
I pressed 3 for Enable Timed Warps with the PageDown and I fell for it.
EDIT: I found the only way. Right click of the mouse get you out of preview mode safely. And get your keyboard back.