Hm. How do you everything plugged in powerwise outside the case? I had an issue with my monitor going black during gaming at times and turned out I was running too much from one cord(pc is on opposite side of room from outlets, so had to run heavy duty extension cords), but once I split it up between a couple of outlets the problem vanished. Might start there.
That would be the first place I'd start man. In my situation, the monitor just went black, but stayed on, the game stayed on as well, and the tower as well. The other things you could try I guess would be check for updated NIC drivers. If none of this works, you could always grab a cheap add in NIC card that fits in a PCI slot.