question: when u plug it in do u hear the NEW DEVICE NOTICE? the sound when u plag new stuff on ur USBs? did u get an error message that ure device is "NOT WORKING PROPERLY" or "NOT PROPERLY INSTALLED" or its totally not detected
1) check if the USB port ur plugging it in is enabled in the CMOS and is USB 2.0 compliant since most new devices/peripherals(mice,KB,webcam,cardreaders) nowadays need a highspeed USB 2.0 to work, if ur mobo is USB 1.1 that isnt gona work
2) have u tried other devices on the USB themselves? check by using other peripherals and try all the USBs u have
3) check is the webcam itself works by plugging it to another PC