An application may remember its last window position after a second monitor has been disconnected. The program can therefore be running normally while its main window appears beyond the remaining desktop. Recover the window with the operating system's window controls before resetting the application or deleting its preferences, because those changes can discard useful settings without addressing the remembered position.
Establish which window needs recovering
Select the affected application through the taskbar, Dock or application switcher. Check whether a small dialog, rather than the main window, is waiting for input. A hidden confirmation can make the visible application seem unresponsive. Do not repeatedly submit commands while trying to locate it, since queued operations may run when the dialog eventually closes.
On Windows, the keyboard shortcut Windows key plus Shift plus Left or Right Arrow can move the selected window between active displays. The result depends on the current desktop arrangement and window type. Another option is the window's system menu and Move command when available; use the keyboard to bring the window into view before placing it normally.
On macOS, check the application's Window menu and any available commands for bringing windows forward or moving them to the current display. Full-screen applications and separate Spaces can change where a window appears. Inspect those workspaces before concluding that the window is missing, and use the controls appropriate to the installed system version.
Restore a useful position and prevent recurrence
If an extra display is still reported as connected, inspect display settings. A dock, virtual display utility or remote session can leave an arrangement that differs from the physical desk. Change only the connection or setting you understand. Removing unrelated display software during recovery can create a second problem and make the original cause harder to identify.
Reconnecting the original monitor temporarily can provide an accessible route to the missing window. Move it fully onto the screen that will remain connected, restore it from full-screen mode if appropriate, and close the application normally. Reopen it after disconnecting the extra screen to determine whether it has saved the corrected position.
Some applications offer a documented workspace reset or window-layout command. Prefer that targeted operation over deleting an entire user profile. Save work first and record any custom panel arrangement, because even a legitimate workspace reset may move tools, inspectors and document panels that were deliberately configured for the two-monitor desk.
Test the same sequence that caused the problem: open the application with both monitors, move its window, disconnect the secondary display and reopen it. If the failure recurs, document the application version and display route before seeking its specific guidance. A repeatable window-position issue can then be addressed without treating a recoverable layout problem as lost data.