Wifi Router: "Internet works, but LAN doesn't work"?

Wifi Router: "Internet works, but LAN doesn't work"?

Hi, I currently had 4 PCs in my house. PC1 = cable connection & PC 2,3,4 = Wifi connection. However, I had configuration issues with PC3 & PC4.

Scenario:
Modem->Cable Router->PC1 (Internet ok & LAN ok)
Modem->Cable Router->[plug 1 LAN cable & 1 WAN cable] to Wifi Router->PC2 (Internet ok & LAN ok)

Problem:
Modem->Cable Router->[plug 1 LAN cable] to Wifi Router->PC3 (Internet ok, no LAN)
Modem->Cable Router->[plug 1 WAN cable] to Wifi Router->PC4 (LAN ok, no Internet)

Enquiry:
Is there a way to configure the PC3 & PC4 connection, so I just need 1 cable from "Cable Router" to "Wifi Router", in order to access both the "Internet & LAN"?