Private Sub cbo_SelectUser_SelectedValueChanged(sender As Object, e As _
  EventArgs) Handles cbo_SelectUser.SelectedValueChanged
    Dim objDR As SqlClient.SqlDataReader
    Dim ConnectionString As String = "DEIN CONNECTION STRING"
    Dim objConnection As SqlClient.SqlConnection
 
    objConnection = New SqlClient.SqlConnection(ConnectionString)
    Dim objCmd As New SqlClient.SqlCommand("SELECT" & _
      "UserName,Kuerzel,Pass,SysRoll FROM user 
WHERE UserName = @User", objConnection)
    objcmd.Parameters.AddWithValue("@User", cbo_SelectUser.Text)
 
    If objConnection.State <> ConnectionState.Open Then
    objConnection.Open()
    End If
    objDR = objCommand.ExecuteReader(CommandBehavior.CloseConnection)
    objCommand = Nothing
 
    If objDR.HasRows Then
    While objDR.Read()
            txb_Username.Text = (objDR("UserName")) 'Benutzername
            txb_Kuerzel.Text = (objDR("Kuerzel")) 'Benutzerkürzel
            txb_Password.Text = (objDR("Pass")) 'Passwort
            cbo_Sysroll.Text = (objDR("SysRoll"))'Systemrolle
    End While
    End If
    objDR.Close()
    objDR = Nothing
end sub