Everything Loses Internet Connection when New Computer is Turned On and Connected

[greelay]

Our household has 6-8 phones, laptops, game systems online regularly. For the most part, it is fine. We have a MacBook that when it is connected, the internet connection goes away for every device. And we have a new computer, and it is doing the same thing. If we turn those devices off and reset the router, everything can come back online, when we start those two devices again, internet connection drops. I imagine that the router is the root of the problem, but why does the issue only occur with two of the nearly dozen devices? Any ideas?

Thanks.

 

[BFG-9000]

This can happen if someone has manually set those devices to have a fixed IPv4 address that's the same as the router's address. Make sure their adapters are set for "Obtain an IP address automatically."