Excel 2003

I have a simple spreadsheet in which I want to calculate some prices.

Along the second row I have number of users (1,2,3,4 etc)

In the row beneath I have the price multiplied by the number of users
(=175*C2 for example).

For some reason when I copy one cell to another, the value of the first cell
remains displayed in the second cell, although the formula has copied over
correctly, so column D for example will display 175, even through the
formula is =175*D2 and D2 is 2 and C2 is 1).

However if I click on the calculation for the cell and click the green tick
the value is then refreshed and displayed correctly.

The problem is I can't go along each cell clicking the green tick to get the
value to display correctly, I need the values to show immediately.

Some setting must have been turned on in my Excel as I know this isn't the
default functionality.

How can I get Excel working correctly again?