very simply
A modem will provide the public IP address to one user only
A router splits the connection up between various devices
so on a modem when you connect a PC to it a do an ipconfig /all - you will see a public IP address
on a router you usually get an IP of 192.168.x.x
A lot of modems with just on connection are actually routers and so going by the IP address you provided in post #3
when I asked you to connect just to the modem
if thats what you did then its a router
i must admit , i'm surprised it worked in the past by just connecting to a standard router
your ISP is correct when it said you need a router to connect multiple devices via wireless as that device does not have wireless ( it would be possible to just use a hub for cable connections)
i would try setting up without DHCP and in the same IP range
looking at post #3
I'd assign the secondary router 192.168.1.254 as it's IP address
Disable DHCP
and connect the modem cable to one of the LAN 1 -4 connections
A modem will provide the public IP address to one user only
A router splits the connection up between various devices
so on a modem when you connect a PC to it a do an ipconfig /all - you will see a public IP address
on a router you usually get an IP of 192.168.x.x
A lot of modems with just on connection are actually routers and so going by the IP address you provided in post #3
when I asked you to connect just to the modem
if thats what you did then its a router
i must admit , i'm surprised it worked in the past by just connecting to a standard router
your ISP is correct when it said you need a router to connect multiple devices via wireless as that device does not have wireless ( it would be possible to just use a hub for cable connections)
i would try setting up without DHCP and in the same IP range
looking at post #3
I'd assign the secondary router 192.168.1.254 as it's IP address
Disable DHCP
and connect the modem cable to one of the LAN 1 -4 connections