Copying inventory numbers into cell in Excel creates havoc

I am creating an Excel spreadsheet with a column that includes inventory numbers associated with photos in a photo collection. Occasionally a number that I copy and paste into a cell results in the cell interpreting it as a date and then presents it as such. How do I turn off this kind of automatic formatting? I've highlighted the cell and tried working with formatting drop-downs in the Excel Home ribbon but nothing I've tried yet seems to work. Very frustrating!