TCPIP Stops, cant suft but can ping

Ok we have been having microsoft consulting us on this and they thus far are zero help. We have a 4000+ user network/domain. We are having fully patched machines randomly dropping off tcpip. The machines can ping out, but you cannot surf intraweb, email, nothing. We ran netmon and seen that tcp service literally stops, ipx keeps running perfect. The tcp service when you force it sends corrupt so it never goes anywhere. Please help me, im pulling my hair out.