ADO, Datagrid and a Combo Box

i have 2 tables linked, one to the datagrid and the other to the combo box, there is a relationship already in place, now i am having problems trying to get it so when the combo box''s selected item is changed, so too is the datagrid to show the correct items. i am at a total loss on how to do this, i have tried to use the selected index, any help???

Loader.
Up arrow icon