The easiest way to check what IP address you are using is to open the Network and Sharing Center. Click on the Connections, such as Local Network Connection, just below the Homegroup option. Then Click the Details button.
Both systems should be the same (disregarding IPv6) except for the IPv4 address and the Network Adapter description..
Another way to get the info is to open a command prompt, so we will open an Administrative command prompt by hitting the Winkey and typing CMD then use CTRL+Shift+Enter to open the window.
When it is open, type ipconfig /all and the information about your connection will be shown.
IPv4 is 192.168.100 on one PC and 192.168.1.101 on the other.
When you refer to Username and Password, you are referring to the one to access the router?
Yes.
In many cases, rebooting all the network devices can help, all the way from your modem/gateway, all the way to your systems. Then start up the modem first and give each device some time to discover the network.