I have a DGL-4500 A1 hardware with 1.02 fw on it and have had it since 07. I've been reading these forums for a month or so now and have had problems with the router rebooting itself alot.
I'm curious, did you operate it upright or flat? I have mine flat, but have a fan constantly blowing air across it, to keep it cool. I keep hoping they will release a unit with a real heat-sink & waste heat removal system. Either a phase-change cooler or a fan.
I had issues with a DGL-4300 and heat, which is why I started using a dedicated fan for the D-Link routers. Your problem actually sounds a bit like what I was having. It turned out mine was due to a failing power-supply, which manifested in a number of issues. I only diagnosed it when I bought a second 4300, and decided to test the new power-supply on the old unit, and all of the strange problems went away. You could try a multi-power adapter (a handy thing to have around anyway) and see if that is your issue. I'd say get a replacement PS from D-Link, but ... I found that process ... unsatisfactory. And I don't know if it's gotten any better in the interim.
Don't know if it will help or not, but I thought I'd add that...
Hank