Q: MacBook Air camera no longer working

Yesterday my Skype was working perfectly , with good video.  Today I could see the caller perfectly but she could not see me.  At this stage I still had a video button on screen but it didn't do anything.  I tried reloading Skype and now I don't even have a video button.  It is as though Skype no longer recognises my computer's camera.  I have the latest up to date software on my mac - version 10.9.4.  Now I find that Photo Booth says "there is no connected camera".  Any suggestions?