Wooh. This question has many answers. The main pc might have more programs or software to make the processor run slower. The second pc might have better hardware components. The routers wireless signals may be excellent with no traffic and the cable and the main pc has traffic. Just a bunch of answers. And check if all the cables are plugged in correctly and make sure they work. When your cable is running slow, you can always reset the router or reset the whole system if its really slow.