OK Ok OK I got it…know exactly what you did to lose it. I just duplicated it and for sure you wont see it.
Open Vegas select pan crop on any media. Watch quickly as the window will be transparent and then move off screen in the direction that you lost it.
It is under the task bar for sure. Click and drag the task bar until it becomes large. Then place your mouse at the very bottom of the screen, click and drag your window back to where is should be. It might take a little practice but I promise the window is there. when you make the Task bar large you just might see the top of the Pan/Crop window. Let me know…I’ll be here
Joe