Hey ho so here I'm back, after wondering what it could be I had no ideo. Changed the wire between my modem and the router, did not work. So I thought maybe changing from D-link to Linksys Cisco ( another top model, the EA4500 ) You know what guys, still wouldn't work.
That pissed me off, I called my ISP and the told me to plug it directly from Modem to Computer, Youtube worked so they wouldn't take care of my trouble.
What I first did, plug back in the Linksys, get into the configuration, it was saying that I wasn't on the iPv6, so I activated it, but the ADDRESS AUTOCONFIGURATION SETTINGS wasn't at the good setting, was asking for an update every 1400sec. I changed it to be like a MAC adress. It did work with the linksys, I had youtube working. SO I thought maybe to try it with the Dlink.
I put back my D-Link DIR-857 Media Server, went into Setup, iPv6 then Manual IPv6 Internet Connection Setup. At ADDRESS AUTOCONFIGURATION SETTINGS Under it, there's Enable automatic IPv6 address assignment Checked, Enable Automatic DHCP-PD in LAN checked, Autoconfiguration Type : ***Put it to Stateful DHCPv6****
And reboot your router. After that it should work, since it is for me !!
Hope it will also work for you