How to Move or Resize an Off-Screen Window in Windows?
This can happen for many reason so it might be best to do a Google Search however, this is the most common fix:
In Windows 10, 8, 7, and Vista, hold down the “Shift” key while right-clicking the item in the taskbar, then select “Move“. In Windows XP, right-click the item in the task-bar and select “Move“.