After using Photoshop 7 for years on Windows XP, my levels adjustment stopped working.
When I select image>adjustments>levels there is no longer a levels control box. The cursor changes as it normally does, but no control box appears. I uninstalled and re-installed Photoshop, and get the same problem.
Thanks! That made sense, that the box was opening up off screen.
I had a box checked in my Nvidia nView control panel that is supposed to 'prevent windows from opening off screen' but that did not help. Then I noticed another option called 'dialog box repositioning' that allowed me to force dialog boxes to open on my display 'number 1' (I only have one monitor connected). That worked! Thanks again.
Can you try gathering the windows somehow? It may have been dragged outside of the standard workspace.