How to replace failed pci fast ethernet net...

How to replace failed pci fast ethernet network adapter in asus k8u-x. Can't connect to internet and I have tried reloading the original driver from the original software disk. Error message says contact manufacturer. PC connects to internet with external network adapter i bought but I have to keep uninstalling the original network adapter each time the pc is turned on and finds 2 network adapters. I would prefer to replace the one on the motherboard than use up a usb port with the external one. The network adapter jack for the internal adapter is attached to a round bulb like object that is attached to the motherboard and can't be removed. Sometimes even the new adapter displays a ping of "loss of 75%." Thanks for any advice. lel