If it is in modem mode then 3 of the 4 sockets are disabled. to get it out of that mode, either do a factory reset, or connect to the one that is still live then you can log in and change mode
.all you need for hub to PC is a standard ethernet cable. For faster than 100Mbs get a cat 6 cable, otherwise cat5e will be fine, and one of those should have shipped with the hub.
that assumes your PC has an ethernet socket but usually that is on the motherboard as standard. it may be 1Gb or maybe only 100Mbs but device manager should tell you that.
but I am puzzled if you are in modem mode you shoudl have no wifi - if you are in router mode you should have 4 working sockets. could be some trial and error needed to determine if you have a faulty cable, or a faulty port on pc or on hub, or if it is just a config issue.
you can connect to 192.168.0.1 from a smartphone / tablet browser to see your hub settings. the login info is printed on the hub case somewhere
what do you see in networks on PC. if you see no (wired) networks available or " no cable connected" then you need to follow the clues..
if you have any strange properties set in networks adaptor properties, tell it to revert to default settings or delete the network adapter from device manager and reboot so that windows re-discovers it and resets it. If the (wired) network adaptor has been disabled then - duh! - enable it !
i think your issue is most likely with the PC settings or components, pictures of the relevant screens will help if you are still stuck.
what version of windows are you using ? and what does device manager tell you is installed for networks