Hi @Henrik Vestergaard,
This issue might happen due to a hidden window because some add-ins, desktop gadgets, or launchers may open a hidden instance of an Office program that disables all subsequent documents opened within the already running instance of that Office program.
I would suggest the following troubleshooting steps.
- Try to open Excel in safe mode and see if this issue still exists.
- Rename the workbook.
Go to File > Save As.
In the "File name" box, remove the "-2" suffix, or any suffix that appears after the file name.
Save the workbook with the corrected name.
- Start Microsoft Excel by double-clicking a workbook or shortcut on the desktop.
Minimize the workbook to temporarily hide it.
Right-click the Excel button on the Windows taskbar, and then click the workbook you just minimized.
Maximize the workbook now open on the screen.
Close Excel, making sure to save all open workbooks.
Restart Excel to verify the issue is resolved.
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