no internet access

[FLarch]

I have a Netgear N600 WiFi Cable Modem Router, Model C3700, that is 4 years old. I cannot get online, I get a message that there is a potential security threat and my browser requires a secure connection. But when I try my neighbor's network, I can access the internet. All the green lights are lit on the Netgear modem. I also have a TP-Link router with all lights on.

Does this sound like the problem is my Netgear modem?  Due to its age, should it be replaced?

[FURRYe38]

Do you have the modem in router mode or modem only mode with the TP-Link router. Router mode would not be recommended on the C series modem if you have the TP-Link router also connected. 

Has a factory reset and setup from scratch with out the TP-Link router online and a wired PC connected to the C series modem. 

[FLarch]

Thanks. However, to set the modem-router to modem-only mode, in order to launch my web browser from my laptop it has to connected to my modem-router’s network.  And that is the problem, I can't get online with my modem (I am now accessing from my neighbor's modem)

[FURRYe38]

 Factory reset and setup from scratch with out the TP-Link router online and a wired PC connected to the C series modem.