Two different things to try:
1) If you have customized menus turned on, turn them off:
a) Select Tools from the Menu bar
b) Select the Options tab
c) Check "Always show full menus"
d) Click [Close] in the Customize pop-up window
2) If that isn't the problem, add it back onto the File menu permanently:
a) Select Tools from the Menu bar
b) Select the Commands tab
c) Select "File" from the Categories list
d) Select "Page Setup" from the Commants list
e) Click and drag the "Page Setup" command to File on your menu bar
f) Drag down the drop-down menu to place the command where you want it.
g) Click [Close] in the Customize pop-up window