The Access Point ethernet port may not be plugged into the network, or the cable may be nonfunctional.
Confirm that the access point can access devices on the wired lan and vice versa. If not verify that the ethernet cable is seated or connected properly to the access point. Check the cable and its connectors for damage. You can also try swapping out the ethernet cable for another cable, or by using a cable from a known working device. If the access point does have connectivity to the wired lan, begin narrowing down othe possible causes sucha as problems with the client to ap configuration. If you have any security enabled (i.e. wep, leap, etc.) remove the configuration and see if the problem persists.
Associated but cannot pass traffic to some devices
WLAN adapters (wireless card) / ACU (Aironet Client Utility)