Look for: ArcSoft Webcam Companion Software in the list of All Programs in the Start Menu.
Also look under the Sony heading in All Programs.
Or you can use the search bar on the bottom of the Start Menu and type in: webcam
OK, I'm betting you did a clean install and wiped out any prior webcam software.
Look on the Sony Support - Downloads and Drivers page for your laptop model and see if there is any Webcam software for download.
Otherwise, you can download Skype, Windows Live Messenger or Yahoo Messenger which can use your webcam.