In order to display the content of an Excel sheet or workbook, it must not be protected with a password when it is opened by AppleWorks.
If an Excel spreadsheet document is protected with a password and then opened with AppleWorks, it displays as an empty spreadsheet. To make the data appear, the spreadsheet must be saved from Excel with the workbook and sheet protection disabled.
Explanations of steps to turn Excel's protection on and off, is offered by Microsoft.