Well, this is not a very big issue, it might happen due to the change in formatting your values are not showing. Check whether the cell might be formatted as Text. For changing it select Format > cells and next on the Number tab> select a category other than Text, for example, General or Number.
It might happen the View Formulas option is turned on. And to turn it off in Excel 2010 follow the steps given:
- On the Excel Ribbon,> click the Formulas tab > then in the Formula Auditing group > click Show Formulas
Or else in Excel 2003, > select Tools>Options. Then on the View tab, remove the check mark from Formulas.
Tip: The keyboard shortcut to show or hide the formulas is Ctrl +` (the shortcut key is above the Tab key on the keyboard)