resetting combo box value in runtime C#2008

Question

hi i am working on a grid view that contains a combo having values populating from database when the grid load data, initially the combo dont have any value(to be attached after rows retrieved) when user select any value and after leaving that row if he wants to deattach the value i want it to be done by using escape key if the user press escape key the combo value should be changed to null/blank as it was originally after retrieneing rows thanks in advance