What is the IP address of your Router?
When "Internet Connection Sharing" is enabled on your Internet Connection, Windows allocates the IP address 192.168.0.1 to the network adapter that connects to the "client" PC. This address must not be changed and ICS client PCs have addresses in the 192.168.0.x range. However, if you have a Router which operates in the same Subnet (IP address range), has the same 192.168.0.1 address and allocates 192.168.0.x addresses to connected computers, then you will have a conflict. In this situation, the Router's own IP address needs to be changed so that it operates in a different Subnet. For example, change the Router's own IP address to 192.168.1.1 or 192.168.2.1 etc.