Self assigned ip address after battery ran out

So my macbook pro has been working out pretty well untill yesterday I was at a friend's house when I ran out of battery. When I got home and plugged the computer the date had been changed to october something 2008 and told me some of my applications wouldn't work because the date had been changed so I tried connecting via wi-fi to fix the date but I noticed it just marked the exclamation mark, and I get this 169.254.x.x which I hear is because there is no connection between the router and airport. Well since then I have been trying to figure out what happened I can't seem to find the reason and it's driving me crazy. things I've tried:

*disconnect both router and modem, and reset router
*manually changing the dhcp numbers on my airport to the same ones on my ethernet connection
*erasing some com.apple files from preferences that I don't remember the names, sorry
*turning firewall on/off
*erasing my keychains and my internet connections and restarting

I don't know what else to do can't seem to find out what happened.
I found this thread: http://www.mac-forums.com/forums/internet-networking-wireless/235607-self-assigned-ip-address.html
where it happened the exact same thing but there wasn't an answer.

Thanks for your replies.

I fixed it!!! OMG so I'm writing this in case anyone is wondering

1.- go to your router address by typing on your web browser something like "192.168.0.0" (it's under your router or you can see it on your ethernet connection),
username and password for login should be under router too.
2.- then go to wireless settings and change your security setting to WPA/WPA2
3.- under wpa/wpa2 setting change to cypher type to AES and PSK to PSK
4.- On network key put the password to your wpa (write it down) and save settings
5.- now look for your connection on airport and it should ask you for your WPA password, write it and you should be set.

well i just tried it right now and it is working hope it helps
my router is a DIR-600 no idea how that even works, it was on my isp webpage