Are you using a router or just the cable modem direct to the computer? You said you were running a P2P program which I have had the same problem as you with some routers… Linksys, Trendnet and some others. The router thinks that the constant ping from the P2P program is either “Ping Flooding” or a DDOS (denial of service attack) and blocks the connection thinking it’s being hacked. This is most likely your problem if you use a router.