Internet Disconnects When Another Computer Opens?

I have a pretty confusing setup. That consists of my main modem router on the living room, then I have that connected to a powerline that is connected to another room, the powerline from there connects to another router that is turned in to an access point, that connects to mutliple computers, a mac and a pc with ethernet. My mac and my iPhone are also connected with Wi-Fi. My main router and my access point are Wireless.So my problem is that, when I open my Mac, my internet will work just fine. But then if i open my pc while my Mac is on, the internet connection is shut down on my mac and works only on my pc, the wireless also shuts down the internet connectivity, it still broadcasts but without internet