Logs would be useful as an nxserver process running at 100% is not normal. Follow the instructions here and submit to issues[at]nomachine[dot]com making sure you reference your forum title.
I would like to prevent nxserver to start at every reboot. Is there a way to do it?
See the image I attached. You can access this via the !M (Monitor) icon in the task/system try and then select ‘Show the connection status’. Click on the on/off button and the dialog should appear.