To help you out. When posting a Question about hardware and it's software problems.
please say the Distro Name and Version. Hardware device and hardware device chip.
open a terminal and as root or sudo. type lsusb to see the usb device. then type lsmod
to see the module(driver) associated with your device.
the reason most drivers for webcams and usb device have been put in the kernel for the kernel.org folks to maintain it.
Your system may have loaded the incorrect module. Or there is a new module for it and you may need to black list an old module. read about quick cam and there linux modules.
and the pixart gspca_pac207 module.
so before you download and build your own modules look in to it.