Watch Window does not work

Clicking on Watch Window in the formula toolbar does nothing. It is supposed
to bring up an Add Watch button. It does not. Cell to watch is
selected...click on Formulas tab in the Formula Auditing group, then click on
Watch Window. Supposed to bring up the Add Watch button and then the Watch
Window toolbar.

However clicking on Watch Window results in nothing happening. I have Excel
on two Vista machines and have the same problem on both machines. Do I need
to "repair" Excel or is there a switch to activate? Any help greatly
appreciated.