By default, when you starts Excel from the Start menu, Excel is started with the Startup screen showing the File->New backstage screen.
In recent version of Excel 2016 (I'm testing with 32-bit Version 1707 - 16.0.8326.2062), when an XLL Excel add-in is installed, Excel start up with no startup screen. In the past, installing an XLL Excel Add-in did not change this start-up behaviour, es expected.
Similarly, if you've turned the Startup screen off (say, as described at https://support.office.com/en-us/article/Turn-off-the-Start-screen-1f2834b4-09d4-490d-9c04-5d9f1b25ff70), then starting Excel should create a default workbook called Workbook1. But, if you have an XLL Excel add-in installed, Excel starts with no default workbook opened.
To sum up, if any XLL Excel add-in is installed, Excel incorrectly opens in the "all workbooks are closed" state (when you start it from the Start Menu).
Detailed steps to create an XLL Excel add-in, install it and test:
- Install Visual Studio 2017 with C++ tools.
- Download and install the Excel 2013 XLL Software Development Kit from here: https://www.microsoft.com/en-za/download/details.aspx?id=35567
- Open a "Developer Command Prompt for VS 2017" and then change directory to the SAMPLES subdirectory of the XLL SDK.
- Rebuild the samples by entering "MAKE.BAT RELEASE BUILD X86" at the developer command prompt.
- Check that the file SAMPLES\EXAMPLE\RELEASE\EXAMPLE.xll has been created.
- Open Excel and press Alt t, i to open the Add-ins dialog. Press Browse and navigate to select the EXAMPLE.xll add-in. It should display as "Example Standalone DLL", with the checkmark next to it. Click OK - a message will pop up indicating that the add-in was installed.
- Close Excel and reopen.
- Notice that Excel has opened with no Workbook, and with the Recent / New backstage display that is normally displayed.
- Create a new workbook, press Alt t, i to display the Add-ins dialog and remove the add-in.
- Close Excel and reopen to confirm that everything is back to normal.
I have tested this with various different .XLL Excel add-ins, including native C++ add-ins like the sample from the official Excel SDK, and using add-ins created with the Excel-DNA library.
The problem was initially reported and discussed on the MSDN forum here: https://social.msdn.microsoft.com/Forums/office/en-US/2bb21bfb-4940-4a68-9656-743ae0b8b4da/bug-in-excel-2016-excel-starts-with-no-default-workbook-or-start-page-if-an-xll-is-registered?forum=exceldev