Enable And Disable Controls Based On Selection In Previous Combo Box

[Excel Fox]

Here's what I've added to your code

Private Sub ComboBox1_Change()

    ComboBox2.Enabled = ComboBox1.Text <> ""
    
End Sub

Private Sub ComboBox2_Change()

    ComboBox3.Enabled = ComboBox2.Text <> ""

End Sub

Private Sub ComboBox3_Change()

    Dim lngCol As Long
    With Worksheets("sample")
        lngCol = .Rows(2).Find(What:=Me.ComboBox3.Text, lookAt:=xlWhole).Column
        Me.ComboBox4.List = .Range("A4:A" & .Cells(.Rows.Count, lngCol).End(xlUp).Row).Offset(, lngCol - 1).Value2
        Me.ComboBox5.List = .Range("A4:A" & .Cells(.Rows.Count, lngCol + 1).End(xlUp).Row).Offset(, lngCol).Value2
        Me.ComboBox6.List = .Range("A4:A" & .Cells(.Rows.Count, lngCol + 2).End(xlUp).Row).Offset(, lngCol + 1).Value2
        Me.ComboBox7.List = .Range("A4:A" & .Cells(.Rows.Count, lngCol).End(xlUp).Row).Offset(, lngCol - 1).Value2
        Me.ComboBox8.List = .Range("A4:A" & .Cells(.Rows.Count, lngCol + 1).End(xlUp).Row).Offset(, lngCol).Value2
    End With
    Frame1.Enabled = UCase(ComboBox3.Text) = "INTERNAL"
    Frame2.Enabled = Not Frame1.Enabled
    ComboBox4.Text = ""
    ComboBox5.Text = ""
    ComboBox6.Text = ""
    ComboBox7.Text = ""
    ComboBox8.Text = ""
    
End Sub

In addition, I've also changed the style of your drop-down box to List-box instead of Combo-box. That way, user cannot 'type' anything that is not there in the list. In addition, I've also changed the Enabled property to false, and based on selection of value in the hierarchical order, the combo-boxes will get enabled.