datagrid dolumn focus

I have a datagrid which i use for entering the item information.

On the first column i have item no, which i want to validate if the item no entered is a valid number by checking the item table.

How can i make the focus stay on the first column if the item no is invalid. Below is the code is use.

Code:

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Private Sub grdDetails_AfterColEdit(ByVal ColIndex As Integer)
Select Case ColIndex
    Case 1
        Dim rstItem As ADODB.Recordset
        Set rstItem = cnn.Execute("select * from tblitems where item_no='" & grdDetails.Columns(ColIndex).Value & "'")
        If Not rstItem.EOF Then
            grdDetails.Columns(2).Value = rstItem!item_category
            grdDetails.Columns(3).Value = rstItem!item_Desc
        Else
            MsgBox "Item number not in the table."
            grdDetails.Col = ColIndex
                     
            Exit Sub
        End If
    Case 4
        If IsEmpty(grdDetails.Columns(4)) Or grdDetails.Columns(4).Value = 0 Then
            MsgBox "Item number not in the table."
            grdDetails.Col = ColIndex
         
        End If
End Select
End Sub

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I can not make the focus stay on the first column. How willi do that?

Another thing. how can i stop user in adding new column if the columns has no data on it?