I just got my new motherboard, Gigabyte GA-73VM-S2, and I installed my Pentium 4 3 GHz with 1GB DDR2 PC2-6400 RAM, the problem is whenever I install my GeForce MX400 128 MB PCI video card or my 5 port USB PCI card my onboard RJ-45 port stops working. I tried my USB PCI card in it with IRQ set to auto in the bios. When I get to Windows, it says "limited or no connectivity". I tried to set the IRQ manually, to about 5 different values, when I get to Windows, it takes about 2-3 minutes until it recognizes the same issue. What is the problem here and how can I get around this? Is my only choice to buy a new PCI-e 16x video card?

Sorry no one responded. Were you able to resolve this?

You said "or my 5 port card" so I don't see how replacing your graphics card will help if the 5-port USB card does it too. Although I think a new graphics card will improve performance significantly over a PCI card, you still have PCI bus problems it would seem - unless resolved by now.