Anytime your network refuses to send and receive data properly , your first troubleshooting step should be to check fof problems with the physical connection between the local computer and the rest of the network. Assuming your network connection uses  the TCP/IP protocol , your most potent weapon is the Ping ulity. When you use the Ping command with no parameters , Windows sends four echo datagrams , small Internet Control Message Protocol (ICMP) packets, to the address you specify. If the machine at the other end of the connection replies, you know that the network connection between the two points is alive.

To use the Ping command , open a Windows command prompt window (Cmd.exe in Windows XP) and tape the command    ping target_name  (where target_name  is an IP address or the name of another host machine ).

If all the packets you send come back properly in roughly the same time , your TCP/IP connection is fine and you can focus your troubleshooting efforts elsewhere. 

Enjoy !