I have an ASA5505 connected to a residential ISP provider. I configured the WAN port as a DHCP client. The ASA recieved no IP address from the ISP.
I then put in a netgear router as my border device and configured the WAN port as a DHCP client. It recieved a IP address from the ISP. Then I configured the LAN port with a DHCP server and connected the ASA WAN port directly to the netgear LAN. The ASA recieved the IP address from the netgear router.
I would like to remove the netgear router and put the ASA as my border device, but the ISP (comcast) residential support people are pretty much useless.
NOTE: I will double check my current ASA IOS, but i am aware of the version update for 7.2.(2).22 and how the ASA wasn't sending a client-id. I already did that update and set the client-id for the ASA mac-address. That didn't resolve the issue.
You might have to call your ISP and have them release your IP... some ISPs only alot you 1 DHCP address with a relatively annoying lease timeout. You can probably wait for it to timeout by having NOTHING attached for a while, maybe reboot your modem OR you could call the ISP OR you could put the MAC address of your Netgear onto your ASA. I did that with my FiOS Service... works fine. HTH