Check that your usb controller is configured correctly, by right-clicking on My Computer, then left click on properties, open up device manager and the usb controller should be at the bottom of the list. Ensure that it is configured with no conflicts.
You need to be running Windows 98, it is possible to configure usb ports under Windows 95, but not many companies bothered to write device drivers for W95, so most usb devices are W98 only. If they are working and you are using W98, try another usb device. If that doesn't work then you may have a motherboard problem or a faulty webcam (I'd try the webcam on another PC if that option was available to you).