I would try connecting direct to modem and see what rate your PC connects to Auto. If 10Mb, then its a issue with your modem. If higher then 10, setting your NIC to hard 100full, and see if any connection issue. Make sure to use the same ethernet to connect modem to PC as you used to connect modem to router.
Once the modem is ruled out, try connecting the WAN port of the router to your PC, set a static IP (192.168.0.2) and try the same tests. If modem > PC are fine, and Router > PC are fine, its probably the Auto negotiate between the two. If it works with old router, I would probably take kargo's advice. If still no go, call Dlink and request RMA.