I upgraded a Lenovo W520 Thinkpad from Windows 7 to Windows 8. Everything worked perfectly. Then I upgraded from Window 8 to Windows 8.1 and I was no longer able to use my integrated video camera with Lync. I tried many different things to resolve, such as updating video drivers, disassociating the video camera from any other app that uses it, upgrading Lync client, etc..
Finally, I stumbled on a fix that worked for my system. I had to re-run the Windows 8.1 Pro installation from the CD due to a sudden, unexpected feature add that I needed to roll back. After running setup again and Windows 8.1 being reinstalled over the existing install, the video was restored to operation in my Lync client.