New installed Ubuntu 20.04 got no internet connection

I installed a new Ubuntu 20.04, but got no internet connection. The PC is connected through Ethernet cable. What can I do?

What I checked so far:

Lights working on both computer and router

Other PC with the same cable works.

Double checked that everything is plugged in correctly.

Running dmesg -w results in a very long list. Idk what were searching for. Maybe this: "link is up - 1gbps/full - flow control off"?

I installed windows on the same PC, with the same cable and internet works.

Lspci says "Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 03)

I can't ping 8.8.8.8

When typing "id a" it tells me things that i don't understand, starting with "1: lo: <LOOPBACK, UP, LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000"

Try to check interface via ip command: This command will list all network interfaces with associated IP-addresses:

ip addr show

Try to find out which one you need(by default enp3s0 or like that). If there is no interfaces but loopback then check output of this command and find your network device:

sudo lshw -C network

If there is your device check config file(first command below). And use second command to apply changes(if there is any).

sudo nano /etc/netplan/01-netcfg.yaml
sudo netplan apply

Example netplan config:

network:
version: 2
renderer: networkd
ethernets:
    enp3s0:
        dhcp4: true

If the interface's state is down(find out from ip addr show output), try to UP it:

sudo ip link set enp3s0 up

Also check assigned IP address from ip addr show output. If no IP is assigned, try this to get network configurations form DHCP:

sudo dhclient enp3s0

P.S. Replace enp3s0 to your interface.