Check the Realtec 8169/81100 Ethernet adapter is not set to run at Auto or 1000Mbps as router will only run 10/100Mbps
If not sure if on how to check the Lan card setup do the following
Start-Network Connection-Local Area Connection -Properties
At the top of display the type of Lan card will be displayed-click Configure- Click-Advanced
In the box listed below click Connection Type – In the value box change the setting to100 base Tx Full Duplex.