Check your router configuration.
There should be something in there showing connected devices.
If you have two devices with the same IP they will generally block each other from working if they try to be online at the same time.
But sometimes you will have one device working and one not, So if you have one camera not working, unplug the others one at a time.
When the not working camera is able to come back online the last camera you turned off is the one with the same IP.