A lan cable can not work with hub but it can work with a PC directly anyone know the problem? thanks

Ok, if it works when you connect PC to PC, but won't work with a switch (nobody makes hubs anymore) then it's a crossover cable See the following website on how to make your own network cable and compare the standards to your cable. If it's A at one end and B at the other, it's a crossover.

Your question isn't clear. What do you mean by "it can't work with hub?" Do you mean you get internet when the PC is directly connected to a modem, but not when it's connected to a hub connected to that modem? LIR

this lan cable is from other hubs(near server) and then go to another room.there is no need modem for internet.i said work this meant PC could connect server speed normally(>50Mbps) but using hubs the speed of PC with same server was very slow(about 1Mbps) thanks your response