So, I got this MacBook Pro 2012 A1278 used from a guy at school (don't worry about the trade). Anyway, I reset everything I could and it didn't work. So, I went to Apple, they will replace it for $125.00. When they pulled up the serial and saw that it was fixed at non-Apple store, they denied fixing it due to non-Apple parts. So, I went to Computer Hospital (Houston, Texas, they said my Wi-Fi was fine, but my motherboard was bad and it would be a $825.00 job. So, obviously I didn't go for it. Since I replaced my RAM before, I had a spare Apple kit and went inside. I ordered a $15.00 Aiport card off Amazon and replaced it. It started working and stopped. So, I tried a Wi-Fi USB (Edimax). Garbage, doesn't work with most Wi-Fi (e.g. like my school). So, I ordered the ribbon that connects to the Airport card to the motherboard and it's currently working at the moment. I hope this will solve the problem!(: