The dialog has probably been moved off the screen. You can move it back on screen by clicking the cross-reference tab, then pressing alt+spacebar & M. Use the keyboard arrows to guess which way you need to move the window.
The dialog has probably been moved off the screen. You can move it back on screen by clicking the cross-reference tab, then pressing alt+spacebar & M. Use the keyboard arrows to guess which way you need to move the window.