Its only the spreadsheet area that has the WHITE screen - a screenshot can't be included because I get the "your account needs to be verified" message and the procedure to do that dead ends without a possibility ( found hundreds of other
users with the same problem )
Excel didn't crash - we can operate menu items and when we click the spreadsheet the cell reference ( like B3 or H3 gets selected ) the content isn't visible.
BUT:
If we first open excel with a blank spreadsheet and the open the .xlsx file then we can load it perfectly. So safe mode isn't necessary I guess.
If we click the .xlsx file from a file-location or from an email attachment then we get the BLANC screen.
The file association seems to be messed-up. Although its a blank new installation WITHOUT ANY older versions of office installed !
On an OTHER computer we have open office installed and there the same file opens perfectly.