Excel 2000

I have a user who has received an Excel workbook as an email attachment. He
saved the workbook to his computer, and then used Excel to open the file (he
did not open the file directly from the email attachment). When he opens
the file, he can view Sheet1, but cannot view any of the other sheets. The
same file, when opened on another computer, works just fine.

Any ideas as to what might cause this behavior?

--Tom