Hi,
1. What is the exact model of the Lifecam camera you have?
2. What are the steps you have tried?
Method 1:
I suggest you to refer the step in the link mentioned below if you have not tried them:
Using Skype with your Lifecam
http://support.microsoft.com/kb/2262196.
Method 2: Perform a clean boot
Refer the site mentioned below:
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/kb/929135.
Note: To place the computer back to boot normally use the step 7 in the same link.