You must first lock all the cells you want to prevent from being changed and then turn on protection.

1. To lock or unlock a cell:
   1. Select the cell(s) you want to lock or unlock.
   2. Right-click the cell(s) you selected.
   3. From the drop-down list, select Format Cells....
   4. Select the Protection tab.
   5. Lock or unlock the cell(s).
      • To lock the cell, place a check in the Locked check box.
      • To unlock the cell, clear the Locked check box.
   6. Click OK.
2. To protect cells:
   1. View the protect sheet options.
      • In 2003:
        1. From the Tools drop-down list, select Protection.
        2. Select Protect Sheet....
      • In 2007/2010:
        1. Select the Review tab.
        2. In the Changes group, click the Protect Sheet button.
   2. Place a check in the Protect worksheet and contents of locked cells check box.
   3. In the Password to unprotect sheet: text box, type your password.
   4. Click OK.
   5. In the Reenter password to proceed. text box, type your password again.
   6. Click OK.