I had internet connection, but when I upgraded my VGA and restarted my PC then everything for eth0 has gone.

When I used ifdown:

 ifdown: interface eth0 not configured

Is there something I could do?

EDIT:

Content of /etc/network/interfaces

auto lo

iface lo inet loopback

When I ifconfig I don't have these lines:

inet addr:192.168.1.5  Bcast:192.168.1.255  Mask:255.255.255.0

inet6 addr: fe80::219:5bff:fe5e:a5e/64 Scope:Link

In the Terminal typed:

sudo gedit /etc/network/interfaces

and then added these lines in the bottom:

auto eth0

iface eth0 inet dhcp

then I typed:

sudo ifdown eth0

sudo ifup eth0

when I send the second command I received the below message:

No DHCPOFFERS received

No working leases in persistent database - sleeping

Any help?