Try the following:
Private Sub CommandButton1_Click()
If ComboBox1.Value = FirstUser Then
If TextBox1.Value = FirstUserPassword Then
Call YourNextMacro
Else: MsgBox "Wrong Password, Re-enter"
End If
ElseIf ComboBox1.Value = SecondUser Then
If TextBox1.Value = SecondUserPassword Then
Call YourNextMacro
Else: MsgBox "Wrong Password, Re-enter"
End If
ElseIf ComboBox1.Value = ThirdUser Then
If TextBox1.Value = ThirdUserPassword Then
Call YourNextMacro
Else: MsgBox "Wrong Password, Re-enter"
End If
End If
End Sub
Code assumes you have combobox1, textbox1, and commandbutton1. Edit it to fit your needs. (I didn't check to see if it works, so post if you have problems).