Jane Weigl

The answer is almost in all likelihood the user is trying to do the upgrade with El Capitan as the Mac OS. El Cap has SIP, so the system integrity protection is preventing a change to the system that could harm it. Disable SYSTEM INTEGRETY PROTECTION. do a google search for proper way to do this. your going to go into TERMINAL, make sure your familiar with how it works. CSRUTIL disable. Didn’t work? you didn’t follow the 4th sentence!

I can confirm that the issue, if you have ruled out all possible chances your internet is actually not working , is in the router. I went loco with this !

the bluetooth antenna can only go one way. the wifi goes to the one that has two next to each other, closest one to the back of computer. then you have a BT antenna that goes NEXT to it, and it mounts closest to back of computer. The BT that mounts closer to the side, it mounts on the front of the computer. both BT mount on the same side the wifi on the other by itself. Its not the end of the world if you get these wrong, you just won’t get perfect coverage, but you’ll connect. Ive used these antennas on MacBook pros with the screens taken off (because the antennas for them are IN the screen)