If I understand your issue corrrect your web cam is not detected . Please provide me some details:
Make and model of your web cam.
Is it a first time installation or it was working earlier.
Do you have a drivers cd for the same.
Thank You for your clarification. Please perform the following steps to bring back your web cam and make it working.
1) Please go to control panel/add remove softwares/select any software related to webcam/and then uninstall it.
Now reboot your laptop and then intall a fresh copy of the drivers and softwares.
If the issue still persists
2) Please do a system restore so that the system get rids of the update that it might have downloaded as update push.