It happened to me on a AP connected to a dsl modem. The modem/router had to be changed because it wasn't working with this dsl line. And it made the Zyxel AP reboot.. Nice..
Try to constantly ping the router and see if stop responding after some time.
In my case, after sending special packets, the AP was going off but nice of him was going on again after 5seconds. Exactly what you need for amule for your ratio
It was also visible using
tail -f /var/log/messages
There were messages appearing in this file at the time of the reboot.
I think it was a dlink also..