It could be a software conflict and maybe the reboot will bring it up for you like it did for me...

Question..(maybe a stupid one) How did you shut the wab cam off when you were done with it? Maybe it needs to be turned back on? (Forgive me if that is a stupid question, I know nothing about web cams but I have had problems when I exited out of something and couldn't get it to work again until I rebooted.)