Boot problems after changing combo drive?

Hi

I have an A1181 Mac Book Duo 1.83 ghz with 1gb Ram. After I replaced the Combodrive when I turned it on the Apple logo appears and the starting sound, then keeps the starting sound appearing like an broken cd and it don´t boot any further. This problem didn´t appear always, sometimes it boot normaly and sometimes you couldn´t turned it on for days. So I open it up again did all the steps for changing the combo drive and after I finished when I turn it on, the screen goes white without the apple logo and the starting sound appears, then it will take 3-4 minutes till Apple logo appears and it boot normal. I can not tell if it starts now always like this because i just opened it yesterday but I wonder if the problem is that something is touching the logic board?