By default, Excel 2010 omits zero if it is present in the first position of cell values. To keep zero as you move to next cell, you need to change the column/row/cell data type into Text data type. This will let you enter zero on first position.
To change into Text data type, right-click the column header and select Format Cells.
This will open Format Cells dialog, from left sidebar, select Text and click OK.
Now you can start entering zeros in column’s cells.
Note: Since it will change the data type to Text, you will not be able to apply any function or formula on this column.