all my dates suddenly appear as the underlying number

[robert4917]

I have built and used this spreadsheet for years.

Suddenly one day all the dates now appear as the underlying number instead of the normal date format....like MM/DD/YYYY

Even when format such a cell as a date it ignores this and the number still appears.

This applies to old cells and new cells input as a date.

[#2]

@robert4917 

automatically changing numbers

Notes: 

• If a number is left-aligned in a cell that usually means it isn’t formatted as a number.

• Depending on the number entered, you may see a small green triangle in the upper left corner of the cell, indicating that a number is stored as text, which to Excel is an error. Either ignore the triangle, or click on it. A box will appear to the left. Click the box, and then select Ignore Error, which will make the triangle go away.

[#3]

@robert4917

Activate the Formulas tab of the ribbon.

Make sure that the 'Show Formulas' button in the 'Formula Auditing' group is not highlighted.