No Network Access on Macbook air either through Wi-Fi or tethered to a phone
I've had similar problems with macbooks. I've found that going into "Network Preferences" / "Location" / "Edit Location" and creating a new location can work.

Here's another option:
set your IP manually to an IP the router will accept, instead of by DHCP. If your other devices connect at 192.168.1.25, for example, configure yours to 192.168.26 (keep it close to other IPs in case your router is set to limit to specific IPs). Apply your changes and try connecting.