Ethernet port

Hi - I just installed Xfinity and have the router and wifi working fine. I would like to hardwire my computer using the house cat5e jacks. However, when I run a cable from the back of the router to the wall jack and then from the wall jack to my computer I get no connection. I am fairly certain the wall jacks and ethernet cables are good (I changed out the cables to be sure). Is there a specific port on the back of the router I need to use?