Story
I recently moved to a new apartment, and at the same time, I upgraded my wifi from a normal/low-end Xfinity plan to their gigabit plan. As part of the upgrade, Xfinity replaced my combination modem-and-router. Since my network name and password stayed the same, most of my devices connected seamlessly to the new network. However, my PC can't detect the new network at all, despite detecting many other nearby networks on both the 2.4GHz and 5GHz bands, and successfully connecting to open networks when I try to.
I want my PC to detect my new network.
Specs
My old modem-and-router was an xFi Gateway (model DPC3939, DPC3941T, or TG1682G), or possibly an Xfinity Gateway - they look the same to me. My new one is an xFi Gateway 3rd Generation, model CGM4331COM. See here and here for the specs of these Gateways. My PC is a Lenovo Lavie Z, running Windows 10 Home. Its network adapter is an Intel(R) Dual Band Wireless-AC 7265.
My other devices are a Mac, a Samsung phone, and a Kindle. They all connected automatically to the new network, and they show excellent signal strength. (I have a second, older Kindle that didn't connect automatically, but it connected at excellent signal strength after I selected my network, entered the password, and chose "manual setup".) My laptop cannot detect the new network even while sitting right next to my other devices. The new network just doesn't appear on its list of available networks.
What I tried
I tried disabling and re-enabling the adapter, with no change in the networks detected. Ditto for restarting my PC while the adapter is enabled, restarting my PC while it is disabled, and turning airplane mode off and on again on my PC.
I have tried editing the adapter's properties (Device Manager > right-click the adapter > Properties > Advanced). The "802.11n Channel Width for 2.4GH" and "802.11n Channel Width for 5.2GH" properties are both on "Auto". I tried setting them to "20 MHz Only" and it did not change which networks were detected. I also tried changing "Preferred Band" from "No Preference" to prefer either the 2.4GHz or 5.2GHz band, and changing "Mixed Mode Protection" from "RTC/CTS enabled" to "CTS-to-self Enabled", but it did not change which networks were detected. The adapter's "Transmit Power" is set to "Highest".
I have also tried each Wireless Mode available on my adapter, again by setting its Properties. The available modes are 1. 802.11a, 2. 802.11b, 3. 802.11g, 4. 802.11b/g, 5. 802.11a/g, 6. 802.11a/b/g. Some modes result in more or fewer networks detected, but it never detects my new network. The 802.11ac value, which is what the xFi Gateways use, is conspicuously missing from these options, but the xFi Gateway also claims to be backwards-compatible with older wireless modes.
I read another SU question where a PC was unable to connect to WiFi due to a conflict between two firewalls. As far as I can tell, my problem is not firewall-related. The firewall on my modem for IPv4 is set to the default "Low", which is described as "LAN-to-WAN: Allow all. WAN-to-LAN: Block as per below and enable IDS IDENT (port 113)". The modem firewall for IPv6 is set to "Typical Security (Default)", described as "LAN-to-WAN: Allow all. WAN-to-LAN: Block all unrelated traffic and enable IDS." I searched for common firewall names (Avast, Norton) on my PC and these are not installed. Windows' built-in "Firewall & network protection" was enabled, but I have turned it off for private networks and my PC still can't detect my WiFi.
21 Answer
What worked
I purchased a USB WiFi adapter (the TP-Link AC1300), installed the driver, and plugged it into my computer. Initially it didn't work: the list of available networks was the same as before. Then, I disabled my internal network card, and the list of available networks changed. Now most of the low-strength networks from my neighbors are gone from the list, but my network shows up at full strength and I was able to connect to it. :)
