Dell Dimension E310 on board ethernet problem

I recently was able to get both my Dell Dim. 8300, and E310 back up and running at full strength, well mostly.  The onboard ethernet connection, (NIC I believe it is), is not even recognized.  I plug the cable from the router into it, just as I have done with the 8300, and nothing is recognized.  I went into set-up, and it is enabled.  If I take an older ethernet card and install that into the E310 as my connection, it connects to the internet without any trouble.  The problem with that is I need to use both of the only pci slots for video card, and audio card as I do not yet have a pci-e x1 video card yet, so I need the internal ethernet to work.  The orange lights are blinking on the port so I believe it is working???