built in camera does not work

jcastel wrote:

Mac OS Sierra

Version 10.13.6 (17G11023)

FYI, version 10.13.6 would be macOS High Sierra, not Sierra. Not an issue.

I suggest that you try the following, in order:

1. Create a new user account on your Mac. Log out of your current user, and then, log back in with the new user account. See if you can access the camera now.  How to test an issue in another user account on your Mac - Apple Support
2. Reset your Mac's System Management Controller:  How to reset the System Management Controller (SMC) on your Mac - Apple Support
3. Boot up your Mac in Safe Mode to see if you can access the camera:  Use safe mode to isolate issues with your Mac - Apple Support
4. Run the Apple Diagnostics to see if it uncovers any hardware issues with your Mac: How to use Apple Diagnostics on your Mac - Apple Support

Please post back your results.

Let's start with a bit more information ... which exact model is your MacBook and which version of OS X or macOS is it running? Was this always an issue or just started to happen? If the latter, could it be possibly be due to a software or firmware upgrade?

What have you done, so far yourself, to resolve this other than just posting here so that we don't try to offer your potential solutions that have not already worked for you?