You may try to enter September 22, 2000 as 9/22/00, but Excel has other ideas about how the date should be displayed. Whether you prefer the style of 22.9.00, 9/22/2000, 9-22, or something completely different, you can leave specific instructions for how your dates should appear.
The style that Excel uses to display your date is actually controlled outside of Excel, in the Windows Control Panel.
Follow these steps to customize the default date style to your liking:
Click the Start button on your Taskbar and choose Settings, Control Panel.
Double-click on the Regional Settings icon, and the Regional Settings Properties window will appear.
Click the Date tab, and you will see an indicator for Short date style. This is where Excel is getting its standard setting for displaying the date.
Choose from several short date styles available in the drop-down list. If the style you prefer is not on the list, choose a style that is close to what you want, then make any changes you want. For example, you can make a two-digit year into four digits by changing the "yy" to "yyyy" or you can substitute dashes or periods for the slashes that separate the month from the day and year.
While here, you can customize the Long date style in the same manner.
Click OK when you have finished entering your preferred date style(s).