kiwis: How can I test to see if my motherboard is the issue?
I have no other PC to connect to see if it's the network cables - WIFI is okay but this machine does not have WIFI 

You can get a USB Ethernet adaptor

or if you are even slightly handy you could buy another network card for your PC..$5 -$15,

or if you are happy with wifi just buy a USB wifi adaptor