I'm having the same problem. I've only had my P768 for a few days. The camera was working when I got it, but now every time I launch a camera app I just get a black screen and then a message saying the app has stopped working. I tried a few different camera apps and all are doing the same thing.
There was a software upgrade for my phone on the LG site. I'm thinking that might be what did it. If I go to About in settings it says Software version P76020e. I'm thinking maybe the upgrade was for P760 and not P768, although it installed without any other problems. I don't know how to undo the upgrade.
I also tried a hard reset to no avail.