[Embarq] Connecting New PK5001A to Old Linksys Wireless Router

I read a lot on here but at 69 brain is not as sharp as it was I thought it was time to get a new modem from Centurylink because I also have bought a new wireless router. I had installed it and it was an TP-LINK’s Archer C7 that is duel band with the 5GHz band I needed because of my out door cameras and they operate on the same band as most all routers and even after making some changes one of them would still shut my wireless Linksys wrt54gs down. My old Embarq modem is a 660 and it does have problems off and on but has done very well operating my Linksys wireless router. When I received my new TP-Link and using it I could never get it to connect to the internet? As for as I know they do not have any tech support and forgot all about you guys. I sent it back and was sent a new one that I have not tried to install yet. I called Centurylink and ask for a new up to date modem figuring that might have been my problem. I didn't know they were sending me a wireless one that is a router and modem all in one. But I can cut the wireless part off and just use it as a modem and router and that I did try. All I wanted to do was let it feed my Linksys for the time being before I installed my new one. I could connect to my Linksys but no internet access. I could also see our home computer but that is far as it would go. The home computer hard wired to the new PK5001A could connect to the net. But even if I plugged in my 50' cable and hooked it up to my newest laptop it would not connect. If I used a new short cord to the new one then it would connect. Maybe like my son told me that my cord might be getting old and need to replace it or put on new ends? But that was the least of my problems. My old Linksys had feed wireless and hared wired all other computers for years. All I want at this time was to install the new modem/router from them and let it feed my old Linksys and I could never get it to work? What I did try after some research was to put their new modem/router in transparent mode and that didn't work but I think I needed to make more changes like maybe change it to PPPoE and not automatic? I have read so much my brain has gone. HA HA. If I can get it to work my old router then with luck it will also work with my new TP-LINK’s. As I found out even with good help from a Centurylink tech was they do not get into the router settings and I was told I needed to get with someone who could help me. So here I am. I know I wrote a lot here but in hopes that one of you are more will understand what I am trying to do and what end I am hoping for and I know it can be done but I am just lost at this time.