Unable to select sheets when maximized

I am running Excel 2007 on a new Windows 7 machine. When both the application
and the workbook are maximized, I cannot click on a tab to select a sheet.
This happens with any workbook, including new, blank workbooks. Sometimes if
I click on the sheet tab several times it will eventually select. Other times
when I click on the sheet tab, I get the Close-Maximize-Restore-Move-etc.
menu. If either the application or the workbook is not maximized, then I can
select sheets as expected.

Any suggestions?
~ Horatio