Need more info. What kind of DHCP server? Is there a router acting as the Default gateway for DHCP and the ZD's Configure/System?
All on one flat subnet, same VLAN?
Can you ping the AP from the ZD's Toolbox/Network Connectivity at the top of the WebGUI, and the ZD from the AP's CLI?
After configuring the AP with 'set director ip a.b.c.d', you need to reboot.
If you setup your ZD's Administer/Diagnostics debug logs for Access Points, it will show if you are even seeing the LWAPP discoveries
when the AP reboots.
Do you see any activity logged on the Monitor/Access Points page, Events/Activities from this AP trying to connect?