Open CMD and type "ping google.com -t", then let it run for a while. Do you get "request timed out" when your net gets dc'd for a short time? Also try setting your DNS to google which is 22.214.171.124 and 126.96.36.199 then enter "ipconfig /flushdns" in CMD.
Also download "TCPView" from Microsoft and leave it open in the background. It shows all processes that are using your net, if a program is hammering your net it will show up there.