Maybe it has a static ip address, could be many things... f you got your AP on your desk just console it
When its booting up break key so you get in the ap boot... (you just need to press any key when its booting up until you see the apboot>
Now here yo can see what config it has.... you can do a print to see the configuration and change it to what you need...
or you can simply do a purgeenv
that command will delete all the config stored on your AP
IF you are plugging it directly to the controller you will needa dhcp server on the controller so it get an ip address... he will see the controller as the master and you will see it on the webview of the wireless controller
If you are connecting it from anther swithc on another ntwork then you willl need to put statically who is the wireless controller and the ip addressand gateway etc if you not provinding dhcp either....
If you providing DHCP and you got a dns in there then you can do something else... now i need a better picture of what is your scenario so i can tell you step by step what you can do...
IF it just something provisinonal i would just do this
get theAP console
get to the apboot
purgeenv
setenv ipaddr 172.16.3.223
setenv netmask 255.255.255.0
setenv gatewayip 172.16.3.1
setenv serverip 172.16.3.221
setenv master 172.16.3.221
Serverip and master ip is the ip of the wirelses controller
saveenv
reset and you will see the ap on the gui of the 2400.
when you finish you can do purgeenv again and well configure it again to your normal wireless controller whatever method you using to provision it... DNS, DHCP etc etc.