Additional information about your setup (OctoPrint version, OctoPi version, ...)these are the plugins I installed - Action Command Prompt, Complicated Apple Watch, Dropbox Timelapse, Filament Sensor NG,Navbar Temp., Octoprint Anywhere,Octolapse, Spaghetti Detective and Thingiverse
First try in safe mode.
If that is ok, deactivate all the plugins you have installed and activate them step by step to find the culprit. You may begin with the webcam related plugins.
When you start in safe mode, all additional plugins are deactivated.
On normal mode, to deactivate a plugin go to Settings -> Pluginmanager.
Here you get the list of installed plugins. On the right side you see two icons. A trash can is to delete a plugin. The other one to deactivates a plugin.
All of my plugins that I added are still disabled. But after a restart just now the camera started working again. i had unplugged it from the Pi to plug it in to a laptop and install software to drive it and make sure the camera had not failed but it seems to be working just fine. So plugged it back into the Pi started it up and i have video again. I will now add plugins one at a time with a restart between each. Wish me luck.