Hi
Sounds a similar to issue which I've been experiencing, although I haven't looked at the event logs as I didn't expect them to survive a reboot, and currently it's disconnected with the Billion back in place.
Interestingly, and this may cause me a problem with the return as they said they will test it and if no fault found a restocking fee is levied, is when it's not connected to the WAN and just has one Wi-Fi client, it's rock solid, and doesn't reboot, or at least I can't make it reboot no matter what I do in the Web interface. It only seems to become unsteady when it's all plugged in actively in use (around 3 or 4 Wi-Fi clients although not all necessarily active as just mobiles or tablets sat idle, 3 PCs, one networked amplifier and a set-top box), which points to a memory issue, and presumably loading the Web GUI and making changes is enough to push it over the edge.
I'll give it a go again later to see if it falls over and what the error message is in the logs.
How many clients do you have connected?
Regards
Phil