Hi Mark,
There is a few different ways to do this. You can copy a blank
cell, then select all of your data, right click and select paste special
and check add then OK. This will convert any text to numbers.
You can also copy a cell with 0 in it and use add or you can also
put 1 in a cell and use the same process but check multiply
instead of add.
The first option is best as it handles any blank cells in your range
however the others maybe better in certain circumstances.
HTH
Martin