I assume the router is connected to the modem and both modem and router are set to DHCP- Auto Config?
First try:
ipconfig /release
ipconfig /renew
ipconfig /flushdns
If not work, try do the same but connected directly to the router via ethernet.
Finally check in the MAC Address Clone tab, to see if the option is enabled.
Note: you access the router page via IE
http://192.168.1.1