Cells automatically overwriting

Hi,

I have recently encountered a problem whereby anything that is entered into Sheet2 appears in that cell of Sheet1 and Sheet3 (e.g. if cell A2 is 2 in Sheet2 it is '2' in cell A3 of Sheet1 and Sheet3, even though those cells may have previously been a different value). This occurs whether it is numerical data, text or formulae that has been entered. I thought it might have been a problem with 2007, but when I reverted back to 2003 the same thing happened.

Is this likely to be something to do with my settings? Any suggestions welcome