Power everything off including the Cable Modem. It is important that the Cable Modem is left without power for a couple of minutes so that the association between your existing connection and the IP address allocated to it is "released". The modem will then recognise a different connection and allocate a new IP address to it.
Connect an ethernet cable between the Cable Modem and the router's WAN port. Connect a second ethernet cable between the Desktop PC's network adapter and one of the router's LAN ports.
DO NOT connect anything by USB!
Power on the Cable Modem and wait for it to be fully booted with four lights. Power on the router and wait until it has booted fully. Then boot the PC. You should now be able to access the router's Setup pages by entering 192.168.2.1 into your web browser. If you are unable to gain access to the router's Setup, you may have to give the "Local Area Connection" in the PC a fixed IP address in the same range as the router, for example 192.168.2.2 with Subnet Mask 255.255.255.0
Does that get you any further forward?