See here for usage example.

Changing look so its not a button

	DataGridViewComboBoxColumn ^DataGridViewComboBoxColumn1 = gcnew DataGridViewComboBoxColumn();
	DataGridViewComboBoxColumn1->FlatStyle = FlatStyle::Flat;

Reading Value

You read the text contents rather than the selected index.  Don't use ->ToString() as it causes errors with nulls.

	if (Convert::ToString(dataGridView1->Rows[0]->Cells[2]->Value) == "")