So i you disconnect the DIR router from the ISP modem and just have one wired PC connected to the DIR router, can you access the DIR routers web page at 192.168.0.1?
Do a factory reset and try accessing the routers web page with IE11 or FF while it's not connected to the ISP modem.
I presume if this fails, then you'll need to return the DIR router for a replacement or contact your regional D-Link support office and ask for an RMA.