RJ45 is the plug connection type for ethernet. Male on the cable, female in the router/modem.
A cross over cable is one that is hardly ever used anymore, that was to directly connect 2 computers, if you look at the plugs and the colour of the little wires is in the same order on each plug, then you are fine. I had included this
link in my original post to explain, but I forgot it on the repost. It explains the difference between a normal (striaght through) ethernet cable and a cross over cable. Chances are this is not your problem if you are only using supplied cables, but 10 second checking can save you a ton of stress if it is.
I assume by clients you mean 'people' clients accessing the network wirelessly and are unable to connect to the internet? I also am assuming you mean the computer that is plugged into the router when you are saying host.
If this is correct, then if you take the USB cable out, no one has internet, but everyone can access the network? If you plug in the USB cable, the computer it is plugged into can access the internet but no one else? If this is the case, then the problem is either
the ethernet cable between the router and the modem or one of the
NIC on the router or modem.
Try bypassing the router by running an ethernet cable from the modem to the NIC in the computer. If this works, then it is your router. If it still doesn't work, make sure the cable is good. If the cable is no good, or looks like it might be a cross over cable then try replacing it. If the cable seems ok, and any other cable you try doesn't work either then chances are your modem is fried in some way.