If you're pasting from a formula, you're probably pasting the result of "" which is Excel sees as different from a blank cell (it's a null value). Assuming you're looking at a single column (if not, you'd need to do this one column at a time)

Select the column, Data> select "Text to Columns", then click "Finish"
This will remove the null values and those cells will now register as blank.
Did that work for you?