Using Microsoft Excell 2000

Have a worksheet with numbers in column E, cells E3 to E10. In cell E12,
have the formula =SUM(E3:E10). Used the AutoSum key to generate the formula
and typed it in manually. No matter, the answer I get is the value in Cell
E10. Can only get the right total if I type the formula as
=E3+E4+E5+E6+E7+E8+E9+E10. What am I doing wrong?