Network Meltdown

Alright guys, I need some help understanding what on earth went wrong with my network last night.

The school I work at is about to do a full upgrade to its network so after hours I plugged various objects into the network (Meraki mx64 firewall, ubiquity cloudkey, ubiquity 500W 48 port switch, ubiquity AP) but then when I disconnected all of these objects I was unable to get the network back online.

the network configuration is as follows: Cox internet comes into the modem, the modem then has a single wire that runs to the router which connects the clients to wireless, attaches to the switches, runs the printer, etc. I thought I would be safe if I disconnected the router from the modem and then connected the new equipment. This isolates the new equipment from all of the equipment on the network, except for the modem. However, after disconnecting all new equipment and plugging the router back in I was dismayed to find that only the direct connection to the modem provided connectivity. I rebooted both the modem and the router multiple times with no result, finally I attached the router to the modem and direct connected into the router at which point the router acted as though it had never been on the network. There was no configuration on the device whatsoever, the password and username were both defaults and I had to completely rebuild the network. Is this device failure or did I have a massive oversight?

If anyone requires any further detail I am happy to provide it, I am incredibly annoyed that things went so poorly and am very interested in better understanding what happened.