Just bought a new router

[mchinjaws]

I recently bought a new Netgear Nighthawk AC1750 that I wanted to use, since it lets me mess with many more settings than the Xfinity Modem/Router combo does. The xfinity documentation said to put the modem in "bridge mode" if using your own router, and I did so, connecting it to my new Nighthawk.

I was able to log into the router gateway and set up wifi names and passwords, but when I try to use it, I don't have internet connection. I'm not recieving any internet connection from my modem, wired or wireless. Also, I'm no longer able to access the modem gateway to change it off of bridge mode. I ended up reseting my modem to factory settings, and getting the internet connection working again. But, I'm still not able to use my new Router.

Any help with this? I don't know why the modem won't work in bridge mode when it should..

[FURRYe38]

AC1750 is not a model#, rather a wifi total speed. What model# router are you referring too? 

What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?

If your ISP modem already has a built in router, This would be a double NAT condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the NG router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the NG router gets from the modem. https://kb.netgear.com/25891/DMZ-on-NETGEAR-routers
https://kb.netgear.com/24086/How-do-I-set-up-a-default-DMZ-server-on-my-Nighthawk-router
3. Or disable all wifi radios on the modem and connect the NG router to the modem, LAN to LAN configure AP mode on the NG router.
https://kb.netgear.com/24104/How-do-I-change-my-Nighthawk-router-to-AP-mode-after-I-ve-already-run-s...