Since yesterday, I wasn't able to open Excel files located on the network which were previously running just fine.

I was receiving errors saying that the file was corrupted or the Excel splash screen was simply freezing trying to open the file.

To add to this strange issue, the same file when copied on my desktop was opening just fine!

I haven't changed anything on my computer. I even tried a Office 2016 repair. So surely one of the Windows Update pushed automatically to my Windows 10!

I have been able to fix my issue by following the steps listed on https://forum.openoffice.org/en/forum/viewtopic.php?f=15&t=42387 (even if I don't have Open Office installed!).

1. Exit Excel.
2. Click Start, click Run, type regedit, and then click OK.
3. Locate and then click to select the following registry key: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\11.0
4. After you select the key that is specified in step 3, point to New on the Edit menu, and then click Key.
5. Type Excel, and then press ENTER.
6. Select Excel, point to New on the Edit menu, and then click Key.
7. Type Security, and then press ENTER.
8. Select Security, point to New on the Edit menu, and then click Key.
9. Type FileValidation, and then press ENTER.
10. Select FileValidation, point to New on the Edit menu, and then click DWORD Value.
11. Type EnableOnLoad, and then press ENTER. Note: The default value is 0 which disables the validation.
12. On the File menu, click Exit to quit Registry Editor.