Spreadsheet Automatically Overriding Date?

Hoping to find some help for a weird issue I am encountering with Excel. I am attempting to enter a date into an already-existing file at work that we are adding to our monthly reports. The problem is that when I attempt to manually enter the date in this cell, it converts it first to a formula and then displays it as 01/01/1900 no matter what is entered.

Has anyone ever ecountered anything like this? Suggestions on fixing it?

Are you enterring the date as =1/1? If you put an equal sign before it, it will calculate it as a fraction