Isight Camera Not Working

[VIKOR]

Hello,i have a iamc G5 and since a couple weeks,i don't know why,my buit in camera is not working anymore,on any application i open,like skype or ichat or any other i always have a message saying "camera already in use by another application,try quit applications...etc..."
but no other application is in use with the camera,how can i fix that??
thank's a lot.