Wireless Network Problems (Airports)

[jyl]

Having a weird problem with my home network.

Set up is Comcast - coax - cable modem - Ethernet - Airport Extreme 11N #1 (prev gen) - ethernet over power line - Airport Extreme 11N #2 (prev gen).

Cable modem is an old Arris, that is not a wireless gateway.
AE #1 is set up to create a wireless network, no security, DCHP and NAT. It lives in the kitchen. The Mac is wired (Ethernet) to it.
AE #2 is set up to extend the same wireless network, no security, router off (bridge mode). It lives in the third floor. The Roku connects to it via wireless.

Started having problems yesterday. AE #2 wasn't working. I hard reset it, finally got it working. Then AE #1's wireless stopped working - meaning, no Macs or iPhones were able to join its network. I hard reset it, power cycled everything from modem to AE's to Macs, changed the wireless settings to add a WPA2 password, took the password off, set up a whole new network, on and on.

Finally I figured out that if AE #2 has wireless "on", no device can join the network. If AE #2 has wireless switched "off", everything is fine - devices can join the network, everything has internet connection, etc. Well, everything is fine except that my wireless signal on the third floor isn't so great, which was the point of having AE #2 in the first place.

What do you think is causing this? Why is this problem popping up now? Any ideas?

I've headed off on a biz trip later today, so I leave the family with no Roku but at least wireless works. When I get back, I'd like to fix this problem. Maybe I'll add WPA2 security as well.

Also, Comcast sent me a new cable modem that is router and wireless access point, I mean to install when I get back. Any issues I might want to anticipate? I'm thinking of double NAT, stuff like that.