Hello Marco,
Thank you for posting your question on Microsoft community forum.
I would like to know some information about the issue so that we could help you better.
Have you made any hardware or software changes to your computer?
I appreciate your efforts towards resolving the issue.
I would suggest you to try following methods and check if it helps.
Method 1:
Run Hardware and Devices troubleshooter and check.
Refer:
Open the Hardware and Devices troubleshooter
http://windows.microsoft.com/en-us/windows7/Open-the-Hardware-and-Devices-troubleshooter
If it does not help, then use method 2.
Method 2:
Please use suggestions provided in this Microsoft knowledge based article and check the issue.
Refer:
Troubleshoot failures to find new LifeCam hardware
http://support.microsoft.com/kb/929087
Note: Serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
http://windows.microsoft.com/en-us/windows/back-up-registry
Also see:
Troubleshooting: Webcams
http://www.microsoft.com/hardware/en-in/help/support/troubleshooting/webcam/lifecam-setup
I hope this information helps.
Please do let us know if you need any further assistance.
Thank you