This is signature behaviour from this router (rebooting). It's also (in my limited experience of a few models) signature behaviour of dlink products, unfortunately.
It's harder to tell if wireless hiccups are the same problem, but when you log into the router and the logs are cleared, the time is reset (if you arent running NTP) and the connection time is reset, you pretty much know.
I did extensive troubleshooting for several weeks to get rid of the reboots about 6 months ago, and then it began again, up to about 10 times a day, combined with hard-locks. So I'm afraid I can't detail everything that I've found to be helpful, because I just don't remember all the little things that I taught myself to avoid in the config.
Aside from trying to have as rational configuration as possible (I view all dlink features with suspicion, so if I don't need them, they get disabled), what I have found is that utorrent and UPNP can cause a lot of reboots. [thats close to a fact, from my experience]. Generally I turn my utorrent settings/connections/pex/dht/ etc down/off/low.
I am running 1.32 NA now, and even though it is much maligned, it is working OK for me with my tweaked config.
When I had had enough of the reboots, I RMA'd that unit [unfortunately, I settled on a working config later]. Humourously, talking to tech support level 1:
Me: This router is rebooting about 10 times a day, and its locking up hard about twice a day.
Me: I've reset to factory defaults, upgraded the firmware, reconfigured by hand, [etc]
Tech support: OK sir what I need you to do is do a hard reset.
Me: My VOIP phone goes through the router, so I'll be disconnected from you if I do that.
Tech support: But we cannot solve your problem without that. It is the first step to get you connected.
Me: I am connected. As I said earlier, it is working at the moment, but the router reboots 10 times a day and locks up twice a day.
Tech support: So what is the problem then?
I kid you not.