When I load POS the invoice screen is missing.

You have enabled resizable POS screen (not recommended) and restarted the PC whiile POS screen was minimized or PC restarted in middle of the night due to Windows Update or power outage.

The first thing you can try is right-click on POS icon running in the taskbar and select Maximize.
If that does not work, follow these steps. 

1. Press Ctrl-F6 Display Properties (even though POS screen is not visible yet).
2. Select Transaction Screen tab.
3. Click on Windows button.
4. Change Left and Top positions to 0, 0 and enter appropriate Width and Height for your monitor resolution (example, 1024x735, 1280x990, 1600x1020, etc.).
5. Uncheck "Show resizeable border". 
6. Click OK, OK to save changes and return to POS.
7. If satisfied with your settings, exit POS and go back in to confirm changes are retained.

It is suggested NOT to enable resizeable window, but press Windows Key+D instead to view the desktop when needed. You can also click the Windows Desktop icon in the Quick Launch bar if Quick Launch is enabled on XP, or click the Windows Desktop button on the lower right end of taskbar on Windows 7/10.

TIP: If resizeable border option is disabled in Display Properties, you will never have this problem again. If problem persists, we suggest you fire the employee who keeps enabling the option.