said by DocDrew:Run a GRC.com Shields UP port test and post the results.
[edit] It's interesting to note, from the way I read it, that the netstat results doesn't show the computer listening on any of the ports originally posted as being used.
What games are being hosted/played?
You said the connection is from the ONT to a switch to your PC. Do you ever connect multiple devices? How?
It's a 5 port switch each device gets a separate public IP.