Go from Start to Control Panel then System>Hardware>Device Manager, find the webcam (probably with a yellow mark beside it) and double click it. Under eth Drivers tab, click on Update Driver and let Windows hunt round teh Net for a new driver.
If that fails, click the Details tab, then scroll to Hardware IDs and note down the four characters after VEN for Vendor and the four which follow DEV for Device. Go to http://www.pcidatabase.com and input those details in the relevant boxes and you should be led to the right manufacturer's site for the correct driver.
It isn't lost unless you un-installed it. Use device manager, device details tab for the device and Roll back the driver. Windows may have updated the driver to something that does not just quite qork right !