What kind of DLINK router are you running the camera on? I have discovered an issue with my DCS-5300G that anytime its hooked to a DLINK router that has NAT endpoint filtering enabled on it , it will stop responding, in my case much sooner than a few days. Actually, the camera was still pingable, but the web interface of the camera would die and I would get 'page cannot be displayed' when trying to connect. The problem would only manafest itself if the camera was accessed from the internet, it never would fail accessing it on my home network. The only way to fix it, albeit temporarily, was to power cycle it, or since telnet would respond, I could reset the camera remotely via telnet. Since you are 60 miles away, see if telnet works for you.
Routers that had an issue for me: DGL-4300 at 1.7 firmware or higher (1.6 worked), DIR-655, DIR-855
Camera was replaced under warranty at one time for this issue and it did not resolve.
Network traces ran during the time of failure show that the camera had closed port 80. Dlink support refused to acknowledge a problem, let alone attempt to resolve it. I ended up returning multiple dlink routers to the store and got a Belkin and it plays real nice with my DCS-5300G and my 6620G