After I started YawCam, the preview screen only gives a bleu window.
I also hear some sound from the soundcard.
As far i can guess YawCam detected the "Hauppaugge TV" card wich also uses WDM drivers.
At some moments YawCam Detect the USB camera and everything works fine.
The USB camera is from Fuji type: Finepix f710 and set to work as an Webcam.
In windows moviemaker i can select the WDM driver i want to use, so i can select the right device. Also some other Webcam software detect the camera right, so the problem must be inside of YawCam.