Power everything off, including the Cable Modem which must be left without power for three or four minutes - this is IMPORTANT so that it loses the association between the existing connection (recognised by its MAC address) and the IP address that it has allocated to it.
Connect a network cable between the router's WAN port and the Cable Modem's Ethernet port. Connect a second network cable between the PC's network port and one of the Router's LAN ports. Power on the Cable Modem and, when fully booted with all lights displayed, power on the Router. When the router is fully up and running, boot the PC. The Cable Modem will recognise a new connection and allocate a different IP address to it.
If you now type the Router's IP address into your web browser you should be able to open its configuration pages to set it up for wireless networking.
You don't need to do anything in the computers that connect to the router, just connect by ethernet cable or 'wirelessly' and they should be online.
NOTE: When connecting via a router, all computers have an equal status in the network. There is no "Host" computer and Internet Connection Sharing *MUST NOT* be enabled on any connection in any of the computers. As you had been using this, disable it again.