Excel formulas don’t calculate

I place a formula into one tab of an Excel worksheet that refers to a cell on another tab of an Excel worksheet. They could be either of two kinds:

=A2
=DefinedName

In both cases, it seems that it’s not calculating the result, and as a default. Very occasionally, it will eventually put in the result, but I don’t know what I did that causes this to happen; in the meantime, it continues to look like the above.

I’ve tried F9 and the Option for ensuring that the calculation is Automatic, but neither changes anything.

Excel 2002, a network installation (so installing an update would be tricky for me to get done unless I brought my own CD in).

Thanks for your help!

Please email: abcs86@yahoo.com with your suggestions while I continue to look for the answer.