The statement below was in the help menu for Excel. Try clearing your formatting in the cells or columns you are changing, then format as text.
Clear contents, formats, or comments from cells
1 Select the cells, rows, or columns you want to clear.
2 On the Edit menu, point to Clear, and then click All, Contents, Formats, or Comments.
Notes
· If you click a cell and then press DELETE or BACKSPACE, Microsoft Excel removes the cell contents but does not remove any comments or cell formats.
· If you clear a cell, Microsoft Excel removes the contents, formats, comments, or all three from a cell. The value of a cleared cell is 0 (zero), and a formula that refers to that cell will receive a value of 0.
Tip To remove all comments from a worksheet, click Go To on the Edit menu, click Special, and then click Comments. Then point to Clear on the Edit menu, and click Comments.
good luck