A number of users recently experienced this - when open an Excel attachment from Outlook or double click on an Excel file in Explorer, Excel starts as blank, the file is not opened.
Probably, a setting of Excel checked - "Ignore other applications that use Dynamic Data Exchange (DDE)". You can find the setting from Excel Options - Advanced - scroll down under "General". Un-check it.
Note: DDE is being exploited and there is higher security risk by leaving this setting unchecked. That may also be the reason why recently this setting is being checked by some security updates.