Hi

if you right mouse click on the cell with the negative number in it and
choose format cells, then under the currency type (numbers tab) you'll see
some options for how you want negative numbers to look - choose the
appropriate option.

alternatively, and this is if you want to use different colours or want bold
to be applied when it is a large negative number etc - and that is to use
conditional formatting
click on the cell containing the number you want to format
choose format / conditional formatting
choose cell value is less than & type 0
click on the format button ... choose a format - click OK

you can add two other conditions if required by clicking on the ADD button -
when you've finished click the OK button again.

Hope this helps
Cheers
JulieD