When was the last time it was working? Did you install or uninstall any software/hardware since then? You can try doing a system restore to check if that fixes the issue.
http://windows.microsoft.com/en-IN/windows7/products/features/system-restore
If you're not able to get it to work even after system restore, you should check if it's listed in the Device manager. Here's how you can check it.
1. Press 'Windows key' + R on your keyboard.
2. Type in 'devmgmt.msc' (without quotes) and click Ok.
3. In the Device manager window that opens up, click on the '+' sign before 'Imaging devices' to expand it.
4. Check if there a red x or yellow question mark on the webcam that's listed under 'Imaging devices'.(
http://support.microsoft.com/kb/310126)
5. If there is no webcam under 'Imaging devices' or the whole category itself is missing, that means the webcam is not getting detected, and you might have to open the laptop to make sure the connectors are all in place. (
Note: If the laptop is still under warranty, opening it might void the warranty. You might be better off letting a technician do this if you aren't familiar with it.)
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