To connect you need to use your remote system account’s username and password (the topic has already been discussed on this forum here: https://forums.nomachine.com/topic/how-to-configue-usernamepassword-authentication).
I tried to tell NoMachine to reset the recorded password. But that still won’t have it ask.
To achieve this – open NoMachine Player, edit the connection file for the Windows computer and check the box “Reset saved preferences and password”. Does that help?
However, “connection refused” shouldn’t be shown as a result of entering the wrong password. Are you sure that the nxserver is running on the server side (the computer you want to access)? Did you do a restart after installation?
After installing you can check the status of the server by clicking on the NoMachine icon in the tray and choosing “Show the service status” (in your case, on the Windows 8 host).