Try closing anything that uses internet i anyway. Skype/AV/Browsers etc. Also, turn of the steam overlay, and if you are using ICS (internet connection sharing) Don't...
But if you must use that, open the ports via the laptop/desktop that is the main connection, and assign the ports forward to the main PC, then assign it to your gaming PC.
Also, try to port forward again, but make sure you assign the ports you just forwarded to the pc you are using.