Two things immediately come to mind. First, if it's happening in *only* one cell of a spreadsheet, check to see if it's set to 'text'. Click on the cell & hit Format/Cells. On the 'Numbers' tab, if it says Text, change it to General.
If it is happening on the entire spreadsheet, click Tools/Options. On the View tab, uncheck Formulas.
Hope this helps.
-Dave