Simple...
When a cell is formated as text and has numaric data in it, changing
the format to number or currency will not work. Even thought the format
in the Format cell pop up box appears to be in number or currency
format.

There are many more ways to convert them to number and some of them are
:

1. Multiply/ divide all these cells by 1 in another Cell or add/
subtract 0.
2. Block the entire column and then do a dataText to column.. Click
finish (without going through all the steps).

3. Later versions of Excel show a green tag indicating a number is
stored as text and helps you convert all such cells into number format
in one go.


Thanks
Karthik Bhat