Network Card Not Working

My desktop stopped working for internet. It has caused me a lot of time to determine what it causes to do so. I bought a cable tester to see if the Lan cable is defective. It turns out that it was not the cable. I have two router used in one connection as connector to my desktop pc and of the office. The two routers are fine as i tested it to desktop computer at the office. The only one left is the network card and as i search for the icon of two computers as used for internet sign is not showing at the bottom right side of my computer and I could not find the network adapter in the Device Manager also. 

I tried to get an update on my network adapter and run the add hardware on the control panel but it could not detect the NIC. I have check the installations of cable in both end. After exhausting myself I decided to but a USB adapter.