I have a spreadsheet that has two sheets in the workbook. Both contain dates in the format dd/mm/yyyy. I have been using this workbook for years. It is in xls format.

Today on opening the second sheet I found the layout (col widths etc) had all changed. More importantly all the dates had changed into numeric values. If I point to a cell, it tells me that it is in date format , and above shows the date in the correct format, but the cell remains a numeric. The other problem is all the cells containing a sum calculation show the formula rather than the result.

All the dates and calculations on the first sheet are correct.

What have I done wrong?