isight and webcam not working with El Capitan 10.11.6

I can

t get mu isight or external webcam to work. My imac is a 2008 ,running El Capitan 10.11.6. Both are listed in the system report. The microphone on the external webcam will work, but thats it. I have tried a number of things: "killall vdc assistant"; restart holding power/shift/control/option to rest smc; and checking to see if any app is blocking access. Even tried to reinstall os, but ran into a dead end. After downloading and starting the install screen, said can't be installed on this machine. Restart and went through same thing 5 times. went ahead and reinstalled via carbon copy cloner so am good with the exception of the isight issues. Any suggestions or other troubleshooting assistance would be appreciated.