Either the system can’t get an IP address, or connect to a domain/workgroup thereby sending continuous requests for ‘whois’ OR you have a spambot in the system and every time you turn it on it dumps thousands of e-mail messages.
Disconnect the network cable – test the IP number. (IPCONFIG) on a different system see if that address is pingable. If so you have a conflict and both machines would fail. Run your antiviru and spyware programs. Manual set an IP address if you have a static value available. IF all these pass then reconnect the cable and see if you can login/connect ot internet etc.
You did not specify OS/hardware so this is very general.