First thing is to get into a shell on the box, via a serial UART or ssh or similar.
Then some of what you want to check is if you can ping out to things on the Internet, eg does
ping 8.8.8.8 let you bounce a packet off google’s DNS server?
If not, you may want to do ifconfig (might in some setups need sudo) to see what address your active interfaces have
And then route -n to make sure that the one that’s actually active is listed as a route to everything (0.0.0.0) and with an appropriate IP gateway, and has the lowest metric.
Sometimes multiple network setups leave you trying to route all traffic through an interface that’s no longer active, either because it’s the only global route entered, or has a lower metric than the one that is active.