Gateway FX6860-UR20P won't recognize any of my Ethernet cables?

I just had my computer looked at by the geek squad, they fixed all the problems I was having with not being able to connect to airport networks. It lasted for about a week and started to decline, I decided to switch over to Ethernet so I route a cable from my modem to my computer and hooked it all up. To my surprise nothing occured, no pop ups, no connection. I booted up my Laptop to see if it was my cable, but when I plugged it in almost immediately it connected, provided better connection then just wireless. I'm not sure what the problem is and I'm not sure wether to build myself a new computer or see if geek squad can help again. If you need any more info just ask

My desktop - http://www.newegg.com/Product/Product.as...