Can't connect to wireless/self assigned IP

We recently moved and I set up my wireless router through my boyfriend's PC. Once we added the WPA password, I have not been able to use airport to connect to the internet. I am getting full signal from the router, but can not connect to the internet. It is giving me a self assigned IP address. When I take off the WPA security I can connect, but the internet is very slow.

Is there some sort of security thing that I am missing, or something I can change on my computer so that I can connect? I tried putting in an IP address myself, but it still will not connect to the internet.

Thanks in advance for any help.