[AccessD] OT reference cells in Excel

Hello All,

In Excel 97 I have Sheet1 and Sheet2.  On sheet2 A1=SUM(Sheet1!A1:A3)...so 
far so good...then I delete the values on sheet1...still good...then I drag 
other values(no calcs just numbers) into the cells on sheet1...here is the 
problem...sheet2 A1 now =SUM(Sheet1!#REF!)?

Help???  Just curious why/something else I need?

Thanks,

Mark A. Matte