why do you need to reset it? Presumably lost connectivity?
Combined with an inability to reset it, that suggests a failed router.
As to its IP address - what does running IPCONFIG /ALL from the command prompt give you? If the router is working, that should tell you its IP address
Personally, despite what you said, I'd bin it. Its a -G series device so must be close to four years old. D-link routers don't last forever - they tend to give up, and failing to respond to DHCP routing requests is one of the first symptoms