I am so lost with this connectivity issue

[azcolor]

I am working with a 2011 Macbook Pro 17"

All of a sudden both WIFI & Ethernet goes out and don't see services in network prefs. Only way to connect to internet on computer is by tethering my iPhone.

Opened up and made sure connections were tight and everything looked okay. Reinstalled High Sierra still the same. Reformatted HD and fresh installed Sierra same - Did it again and installed El Capiton Still the same.

It was at this point I was thinking I needed to replace hardware when........

Took out a USB Drive with a old Backup I took with Carbon Copy Cloner that has Sierra as the OS and booted from the external drive. Everything came up and works perfectly.

Can't be hardware but why will it not work when I fresh install any of the versions of OS X?

Anyone?

 

[honestone]

Given all the issues folks have raised here about High Sierra, it's not surprising that you would have issues. But with fresh, clean installations of Sierra and El Capitan, and with the issue still occurring, that is baffling!

Do you have a robust disk cleanup/maintenance/repair program like Disk Warrior or Tech Tool Pro? Using one of them to check out your internal drive would be helpful. If you don't have either of them, you could do a restore from the Carbon Copy Cloner backup, and if the issue comes up again, that would most likely mean there is an issue with your internal drive.