A recent Microsoft security update has caused problems for some users when they attempt to export or open a printable view of a Salesforce report.  The resulting Excel file appears as a blank/gray screen with no data.

This should be fixed in the latest release from Microsoft - https://support.microsoft.com/en-us/kb/3115476.  However, if it is still not working properly please continue reading below.

The recommended workaround is to show the downloaded file in the folder (this option differs between browsers).  Then right click on the file and choose Properties.  Finally, check the Unblock option at the bottom of the Properties window for the security.

This is a know issue and hopefully it will be resolved in a future update.  The link below contains further details and other potential workarounds.

https://success.salesforce.com/issues_view?id=a1p3A000000IZSEQA4