We need more info then just "Have tried & failed to set up my Actiontec Gateway & adapte to connect to Internet"
Have you tried connecting your gateway to your modem and then wiring your PC to the gateway and see if that works? You need to narrow the problem. Once you have connected via ethernet cable to your gateway, log into it and set it up. Are you using PPPOE or Static IP or another configuration? Your Provider will tell you if you dont know. You will have to initially set your gateway for those setting and place your user name and password in it, if not a static IP.
Once you get your gateway working via wired networking, then progress to the wireless step.