If number formatting a cell has no effect on the appearance of the value in the cell, this is likely caused by "Numbers Stored As Text". In other words, the value of the cell is not actually a number, but Text that looks like a number...
to test, use
=Isnumber(A1)
To resolve, type a 1 anywhere on your sheet, copy it.
Highlight offending column, paste special - values - multiply.