c++ builder tstringgrid problems

im using a tstringgrid to make a sudoku game
im using goEditing = true with a few loops and its working fine so far.
i have a form with a tstringgrid and a tcheckbox
what i want to do now is have the tstringgrid be fully editable then when the user has inputed the initial values he clicks the tcheckbox and then every value previously entered is no longer editable and changes there color leave only the empty cells editable

is this possible i cant see anything to prevent only certain cells from being editable or change there color

thanks