When I turn my firewall off Internet works, but if I turn it back on, I will lose internet connection.

Hey guys!

The past two days my WiFi has stopped working. I can still connect to networks and personal hotspots, but they will have an "!" beside them and then they will say, "this network has a self-assigned IP of (*insert network IP here*) and therefore cannot connect to the internet." I ended up going through to my System Configurations folder and deleting all those files that are like "com.apple.networking.ptst" or something like that. It ended up not fixing anything, so I was going to try to completely erase my Macbook, which I again was unable to do because I had no internet connection to disable Find My Mac. I finally on a whim decided to turn my firewall off and the moment I did so, my internet began working again. If I turn my firewall back on, I will lose internet connection. This happens to all networks and hotspots I have tried to connect to, so I know it is for sure a problem within my computer. Luckily I have it fixed for now, but I hate leaving my firewall off. Any suggestions?

[Re-Titled by Moderator]