7i97 no ethernet connection

There are no ethernet connection between mesa card 7i97 and the computer.
I tried it with two differents computers (Asus i3) and (HP Elite 8300 i5), both with fresh instalation (LinuxCNC 2.8.2 Debian 10 Buster PREEMPT-RT ISO)

Both computer have good conection to internet throug Ethernet but 7i97 failed to comunicate with both computers, same messages 

1º power supply the Mesa Card 7i97

2º It seems the card try to connect but something fail and I get:
Connection lost
No longer connected to 802-3-ethernet 'Wired connection 1'

3º If ping 192.168.1.121
connect: Network is unreachable

Please could anybothy help me, I am running out of ideas !!

/etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

I don't remember everything, but, I recall I had to go to using Network Manager (Net Man). If you are not using that you probably want to. There are threads here on Net Man.

Also I installed a secondary WiFi NIC for the Internet and am using the built in NIC for the Mesa. That way the Mesa could be connected directly without a switch, as recommended, and I could get to the Internet for updates & such via Wi Fi.

wiki.debian.org/NetworkManager

I've done what is described in Network manager, editing the interfaces, etc.
But no luck
Something is clear that in my two computers network manager are not working properly , if I click on the connection and then edit.....nothing happens
Thanks Jack for the input!

Use Network Manager  -OR- edit the interfaces file, NEVER BOTH.
Now it will be easier and faster to do a new install.
What does in a terminal say ?

arnoldo@arnoldocnc:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp2s0f1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 38:2c:4a:34:67:b9 brd ff:ff:ff:ff:ff:ff
arnoldo@arnoldocnc:~$