Ok, here is my take.  Background (15 years Sr. Network Engr. JCPenney) On P55 FTW that I have, there are 2 ports, so I have 1 of them turned off.  On your board I believe you have only 1 LAN port.   You said you have Intel LAN Port? Is that what is showing in Device Manger under LAN adapters, clicking on it should show you which chip model you have so you can get the lattest correct driver?  Now under my system (Marvell) I have an Advanced TAB, I click on "Jumbo  Packet" make sure your value is 1514.  Also, "Wake From Shutdown" should be OFF.  Go to drive and write down the Provider, DATE, and Version for later use. 
 
Next to see where your packets are going use the "router -4 print" command. 
This should give you on the first line (no quotes) "network destination", "netmask", "Gateway", "Interface", "Metric" .  So next line just below will be "0.0.0.0" "0.0.0.0" "192.168.xxx.1" "192.168.xxx.2" "20".  Now the 1st (Gaterway address)  xxx will be your default network (or your choice if you have yourown router), this is normally 001 or 002.  The Interface's xxx should be exacty the same value and USUALLY (default) 002 as this is your PC LAN value.  If you have defined yourown network the Iinterface value can be whatever you chose in your router's DNS. 
 
Further down you will see your complete network info, which under the "Netmask" should have a value of 255.2555.255.0
 
Now I will post a method of how to make sure you only have 1 driver present on your LAN interface.  Since you have installed many of them, supposedly unused / remove drives will be hidden. 
 
You may want to check and see if your old drivers  actually got removed.  Device manager will not show them.  
To check and see if you have extra drivers from re-installs present on your hardware; you must set a flag for device manager from the cmd box.  In the Start Menu, click on All Programs and then Accessories.  Now right click on the Command Prompt and click on Run as administrator.    Now type in this  FLAG/CMD:(do not type the FLAG/CMD:)  “set devmgr_show_nonpresent_devices=1” (no quotes) 
Next type ”devmgmt.msc “  (as administrator)
Once you are in Device Manager, go to the "View" menu, select  “Show Hidden Devices”.  This will show all the device drivers including things that aren’t currently installed in your computer.
You can right-click on the driver and then choose Uninstall from the menu to remove the drivers for that old hardware.
This procedure can resolve a lot of weird issues, and even increase performance on some machines where you’ve upgraded drivers a ton of times.  
NOTE: the grayed out drivers may OR may Not still be needed.  Before deleteing make sure they are not for some devices (like USBs or some parts of media player).  
 
Now all that being said... PM me if you want or need any more help.   I would start by removiny your new network card and see if you can get your built in chip to work.  If not the be sure to shutdown that chip in BIOS, then remove its drivers and go for the new card.  Good luck