Hi, I've got the same laptop as you, and occasionally get the same problem.
What fixes it for me is to go to:
1) Start Menu > Control Panel > Device Manager > Imaging Devices
2) Under Imaging Devices, you should see something like "Sony Visual Communication Camera VGP-VCC4"
3) Right click it, then click "Disable". Wait for it to do its stuff, then go back to it, right click, "Enable".
4) Again, let it sort itself out. If it prompts you to reboot, do it.
After that, you should be fine. I find that the problem happens whenever I need to use my webcam on Windows Live Messenger, so I do the steps above and it works for me.
Hope that helps you.
Cyprino
