Ok, I would start over, do a factory reset.
Use 1 PC and connect the pc to the 657. Don't connect up anything else and don't connect the 657 to anything else, just you, PC and 657.
Now to set a static IP address on the PC so set up say .49 and use same sub net mask.
You should be able to follow the steps in the sticky. Just turn off everything, SPI, and and all filters, uPnP, Traffic Shaping WISH, WPS things like that first. Save and reboot. Then go in and set up the Wifi. Now SSID and password can be the same however you need to manually set a Channel that is different from all the others. So I recommend if you use channel 1 on the main host router, use 11 on the 657. Save settings and reboot.
Now lastly, change the IP address of the router to .50 and the subet mask and gateway should be the same as the host routers information. Save and reboot. You still still have access to the 657 using the new IP address.
If so, then power off the 657 and reset your PC back to Auto obtain IP addressing.
Connect the 657 to your main host router using the LAN port in back. DO NOT USE THE WAN PORT!. LAN to LAN only. Power up. You might want temporarily turn off the WiFi radio on the host router to test the 657 in AP mode and ensure devices are connecting properly to it and getting internet access.