Unfortunately, I can't give you the exact solution to fix it, but I have some suggestions. I had the same kind of problems while setting up my own mining rig, so wish you good luck with that.
Check if the problem is caused by specific PCI-E slots. If not, you should check the Risers to verify that they are all working without any errors. So far so good?, then I believe you have something wrong with your softwares (OS, Drivers, etc.), which is better because software-sided problems are eaiser to fix. I think you can test it out by using Simplemining OS, since it doesn't require any software setups, tweaks and etc, it should be eaiser to check if all cards are recognized by your os and working well. Other than that, you can uninstall your graphic card drivers with ddu and plug them one by one (restart per every card plug.). If none of these are working for you, as a last resort, you can check your bios settings. check youtube videos to see if you have a missing configuration or something wrong with your settings.
The information you've provided is so little, so all I can do is to give you some advice and make assumptions.
The information provided is pretty much all that is needed. Code 43 in the mining space if it was working before and just started code 43 means a dead card. Theres really 2 steps before saying its dead and that is Check connections and power, reinstall drivers. If neither of those work, then it is a dead card.
GTX 1060's die easily when being pushed too far especially the 3gb. It will run stable for a while then die. The system had too high of an OC, and killed the card. You need a lower OC, or you will see more 1060's dying.
