Dependent combobox to provide matching row count based on 3 criteria

You can change the combobox1 code

Private Sub ComboBox1_Change()
    Dim ws As Worksheet
    Dim LstRw As Long
    Dim Rng As Range
    Dim c As Range
    Dim cUnique As Collection
    Dim vNum As Variant

    Set cUnique = New Collection
    Set ws = Sheets("Install Database")
    With ws
        LstRw = .Cells(.Rows.Count, "B").End(xlUp).Row
        Set Rng = .Range("B4:B" & LstRw)
        Me.ComboBox2.Clear
        On Error Resume Next
        For Each c In Rng.Cells
            If c = Me.ComboBox1 Then
                cUnique.Add c.Offset(, 1).Value, CStr(c.Offset(, 1).Value)
            End If
        Next c
        On Error GoTo 0
    End With
    For Each vNum In cUnique
        Me.ComboBox2.AddItem vNum
    Next vNum


End Sub

Use this formula to find the matches of all three comboboxes, it uses the linked cells you have for the comboboxes

Formula:

=COUNTIFS('Install Database'!B4:B16,"="&C2,'Install Database'!C4:C16,"=" & I2,'Install Database'!D4:D16,"="&N2)