For whatever reason the express isn't shown on the left of the screen with the extreme - which I guess means the extreme is not picking up the signal of the express?
That's not correct. In order for them to appear in Airport Utility next to each other, they have to be on the same network. If AX has not joined the AEBS network with the correct credential, then you will not see AX on the list. Think about the security implication, and you don't want your neighbor's base station to be listed on your Airport Utility either 😉
Do a factory reset, your AX will create a new wireless network. Follow my procedures above, you should then be able to switch to the new network. Once you are on the new network, make the AX join or extend a existing wireless network with the correct security and password.
Message was edited by: dchao99