Joanne,
You can only tab to cells that are UNLOCKED after protection.
Make sure the sheet is NOT protected. Select all the cells that you
want to be able to change when the sheet is protected (i.e. cells w/o
formulas, titles, or column/row lables), click Format>Cells... (Ctrl +
1), go to the Protection tab, and make sure that the Locked checkbox
is unchecked.
hope this helps,
Conan