@drnick5, I mentioned Killer specifically here, because the firewall is actually built into the NIC driver itself, and it's VERY EASY to miss that it's there.
I don't think that's the case here, because a USB NIC would have bypassed it.
My next suggestions would be to example the TCP/IP stack common SSL faults... system clock set correctly? Have you run a memory diagnostic? Have you pulled the drive and used something like DBAN on it? That may be required to remove some forms of malware that can actually persist beyond a nuke and pave.
But I'll admit, I'm grasping at straws on this too.
*Edit* I just looked up that unit and it's equipped with an RTL8111G LAN adapter, that's a SOFTWARE adapter... so if you have a flaky memory stick... it will react very poorly. All USB interfaces fall into this category as well. So I'd be checking that RAM! If the unit has an SSD in it, it can ALSO cause this behavior for the same reasons.