My $0.02...
- Have you tried another Wifi computer on your router? Is the WiFi router going up?
- Have you rebooted your router/modem/etc. recently?
- You could try blowing away your network related plist's. They may have become corrupted.
- You could try AppleJack diagnostic and repair tool -
http://www.macupdate.com/app/mac/15667/applejack- Self assigned-ip is rarely a serious problem or hardware issue. Most likely a corrupt config or incompatibility. I even had it on a Windows XP laptop until I updated the firmware on the WiFi router. Weird thing with yours though, is it was working at one time.
- I wouldn't worry about the PRAM/NVRAM/battery, OS X doesn't store any information their and definitely not your MAC.
- You didn't give a lot of info to assist with troubleshooting. Have you changed or upgraded anything recently? What version OS X are you running? What's the make/model of the WAP?
Good luck
