Need Help with XP OS and new service

[bigdog15050]

Yesterday tried helping a neighbor get internet service going with a computer I gave them. It is XP OS. The jack in back of computer does not work!!!!   It connected for the first try with my  Verizon  modem/router. They have "new" service (yes it's active) but no computer. So I gave them a old XP that belonged to a friend who passed. Spent 6 hours there yesterday and 2 or 3 calls to Tech. support with no luck. Actiontec modem/route.r We enter the default user name and password,,,, long pause,,,,,, and No connection. Anyone know XP well enough to offer help? I'm thinging computer config. is issue?  Any XP user advice would be great.

Thanks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!