I've been dealing with a sporadic boot problem with my QNAP 859 pro for about 6 mo now. I've been on and off with support as I've found time to try and address this problem. Even returned the unit and had the motherboard replaced. However I think we finally tracked down the problem with this last attempt! A memory problem!
I had to load up TeamViewer so the QNAP support team could access the NAS from my machine and emulate the problem where any type of sustained transfer of data caused the QNAP to reboot. The support guy ssh'd into the QNAP box and uploaded a utility called mem_stress. He then fired it up and voila!, the QNAP rebooted after 2 mins. I did it myself two more times and the box rebooted after 19s and then 6mins respectively. So it appears as though this is the culprit! Anyway, I'm in the process of returning the unit for a second tune. It'll be so good to have this unit actually functioning and in production.
On another note, TeamViewer worked really well! No port-forwarding or advanced setup required. Just install, enable full access and anyone with the session ID can connect to the machine. There are a multitude of settings to customize what can and can't be accessed as well as allowing a VPN connection. I'll have to play with this a little more as it may just work perfectly when I need to help out a friend in need.