If your Zoom screen disappears, it may be that you have switched to another application on your computer. Look at your taskbar at the bottom and look for the blue Zoom symbol. Click on it.
If this doesn’t fix it, you may have accidentally minimized the Zoom screen. Check to see if there is a small window on the upper right of your screen. Hovering over the bottom of this window will provide you with an icon to exit minimized mode.