Lock and Protect Cells Containing Formulas - EXCEL 2007

Select Cells contain Formulas in Sheet, Select Data -> Data Validation. Now you will get a Dialog Box of Data Validation. Select Settings -> Validation Criteria, select Custom from the Allow: box, and in the Formula box, enter ="". Click OK

To Unlock and remove protection from Cells containing formulas
Select Data -> Data Validation. Select Settings -> Validation Criteria from Data Validation Dialog Box. Select Any Value from Allow: box and Click OK