The random reboot can be caused by a number of issues. I'll start with a few based on the minimal info you've provided:
Have you run memtest to confirm RAM stability?
Have you run OCCT/Prime95/3dMARK03 or 05? How are your 12V rails?
Based on the info I gathered here bfore my build, I did not install the nVidia firewall. I used a router to provide that service, even before I bought a DFI board. If you uninstall the Active Armor (firewall), is the machine stable?