Have searched all over the internet for solutions to this for days now, but need someone with a little technical knowledge to help.
Macbook 7,1 (2010) with 10.9.2 installed. My internal camera now intermittantly works (likewise under 10.9.1), so I'm confident it isn't a hardware problem. When it doesn't work I get the black screen in Facetime 'No Camera Available'. A hard / soft restart / shutdown does not solve this, nor does resetting PRAM nor SMC.
When I use sudo killall 'VDCAssistant' or 'AppleCameraAssistant' then Terminal tells me there is no such process. I have also deleted keychains, verified permissions (for some reason my printer permissions change, even though Im not connected to a printer nor attempting to print anything, but I think thats a red herring). I have deleted preferences and passwords and Internet Accounts. I have logged in and out with my Apple ID in every available way, through the website and App Store, Itunes, you name it. Messages app included. I have tried connecting other (digital rather than webcam) cameras via USB and run iPhoto. I have tried running VLC, Google Hangouts, Skype, all of which were consistent with System Profiler : There is no video capture device.
When I have gotten the camera back online, I'm not entirely clear what has solved it.
What I do know is this : in Facetime my 'preferences' option is greyed out. Further, when I select 'Turn Facetime On' it greys out and never completes. So what is Facetime doing at this point? I had noticed that it wanted a password from me when I first upgraded to OS 10.9.2 but that hasn't happened since.
One assumption might be that the OS is failing to load some sort of driver for the camera at start-up, but this wouldn't explain why it sometimes works, sometimes doesn't (I don't vary the content of my system, its the same apps on there all the time). Another idea might be the widely suggested one that there is a process failing to be killed by another app, and given that the OS doesn't allow two apps to share the same camera, the solution is to kill the process. However a little detective work with Activity Monitor / 'top' in Terminal doesn't reveal any obvious processes linked to the cameras operation. So why is System Information not able to find the camera? That seems like a driver problem, to me anyway.
I see a lot of folk are having the same problem. I'm currently touring South America, so fixing this would be a big help to me.