You've just moved the text generator window off the screen. I don't know why you can't find an answer, it's answered on this forum regularly. One of these should work (not sure which)
1. If you're running Vegas Pro, press Alt+D, D to get the default layout.
2. Start up Vegas by holding down Ctrl+Shift when you double click the icon - this resets most windows to their default position
3. Change your screen resolution in Windows. Start Vegas. You should now be able to see the Gen Med Window. Move it. Shut down Vegas. Change screen resolution. Restart Vegas.