well, simple test: transfer the footage from lacie drive to local drive, disconnect all external drives, Vegas will ask you to point to new location, and can rerun render.
that at least will get the FW out of the equation.
2nd: good PSU?
3rd: good RAM? try removing all except one stick, make sure is seated properly, then rerun render. Try the other sticks with same logic.
4th: have any nested projects? remove and try render
5th: create new timeline, drop some of the NEO footage thereon, and try new render – just to see if any clips causing particular problems.
6th: try render using footage from someone else’s external drives, just to get your Neo stuff out of the equation.
Is simple process of elimination. Am guessing it’s either codec or hardware related – not windows itself.