Problems with tdm-trinity

Hi, I will setup a Lenovo T410i laptop which has a nvidia grafic card. The laptop should use additioaly second monitor when in the docking station and of course expand the gui across both screens. The (original) driver can't handle this - allways assumes both motiors are connected. So I installed the nouvea driver and get trouble with tdm. Tdm starts and I see the clock for a short time and then tdm terminates and a text only terminal login is shown. When login and call "startx", I get a working trinity session and the crash report manager is shown. So my question is "where can I look for error messages of tdm" or has some one else an idea or a solution for the problem? Many thanks in advance Rolf