What sheet is the linking supposed to be? Normally, one plays a macro from the activesheet that the userform interacts with. If I am not told what sheet, I have to assume one.
Since the linking happens, you should remove the textbox change events unless you need more than link updates.
As a troubleshooting tool since you did not do the labels like I did, you can use this to doubleclick and see the active linked cell address.
Private Sub TextBox1_DblClick(ByVal Cancel As MSForms.ReturnBoolean)
MsgBox TextBox1.ControlSource
End Sub
If you want my code to link to cells other than an activesheet, you need to set it. Here are what has to be changed.
Private Sub ComboBox1_Change()
Dim r As Range, i As Integer
Set r = Worksheets("H-erne").Range("D3")
Select Case ComboBox1
Case 1 To 7
Set r = r.Offset(, ComboBox1 * 3 - 3)
For i = 1 To 3
Controls("TextBox" & i).Visible = True
Controls("TextBox" & i).ControlSource = r.Offset(, i - 1).Address(external:=True)
'Controls("Label" & i).Caption = r.Offset(, i - 1).Address(False, False)
Next i
If ComboBox1 = 7 Then
TextBox3.ControlSource = Range("X3").Address(external:=True)
'Label3.ControlSource = Range("X3").Address(False, False)
End If
Case Else
End Select
End Sub