It may have some problem as below
1.Another webcam use too much USB bandwidth.
Please remove the webcam form your windows as below.
And then reboot your PC.
2. Your Grabber card had been used by another software
At the same time, grabber card only is for one software.
If your Skype let your grabber card work, MSN can not use at the same time.
We can use the easy way to judge if grabber had been used.
If the grabber card's light turn on, it means some software had been used the grabber card.
3.Another USB Device hold the USB bandwidth.
For example, 3.5G usb dongle card will hold the usb Bandwidth. It may let grabber card not to work.