Setting up a home network...HELP PLEASE!!

Ok, my mom bought a new desktop, and were wanting to make a network where I would be using an ethernet card, and she would be using a card as well. We have the router installed, and I can get online, but for some reason the card isn't working right. The laptop for some reason isn't getting a signal when I unplug it, and as soon as I unplug the ethernet cable , the computer goes offline....I'm having a ****ing ****load of trouble with this card...can anyone help me out here??

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