To test a Windows XP computer's connectivity to your router:

1. Go to Start>Run
2. Type in cmd and press Enter
3. Type in ipconfig /all and press Enter
4. This will return something like the following.  The information you need is in red:
   
   C:\Documents and Settings\User>ipconfig /all
   
   Windows IP Configuration
   
           Host Name . . . . . . . . . . . . : User
           Primary Dns Suffix  . . . . . . . :
           Node Type . . . . . . . . . . . . : Unknown
           IP Routing Enabled. . . . . . . . : No
           WINS Proxy Enabled. . . . . . . . : No
   
   Ethernet adapter Local Area Connection:
   
           Connection-specific DNS Suffix  . :
           Description . . . . . . . . : Broadcom NetXtreme 57xx Gigabit Cont roller
           Physical Address. . . . . . . . . : 00-11-43-C6-35-BD
           Dhcp Enabled. . . . . . . . . . . : Yes
           Autoconfiguration Enabled . . . . : Yes
           IP Address. . . . . . . . . . . . : 192.168.1.100 (This is the IP [Internet Protocol] address of the computer.  It obtains this from the router)
           Subnet Mask . . . . . . . . . . . : 255.255.255.0
           Default Gateway . . . . . . . . . : 192.168.1.1 (The IP address of the router)
           DHCP Server . . . . . . . . . . . : 192.168.1.1
           DNS Servers . . . . . . . . . . . : 72.4.58.20
                                               74.137.0.52
                                               74.137.0.53
           Lease Obtained. . . . . . . . . . : Saturday, May 12, 2007 9:29:43 AM
           Lease Expires . . . . . . . . . . : Sunday, May 13, 2007 9:29:43 AM
5. You can attempt to ping the router from the black command prompt window (cmd window) by typing ping 192.168.1.1 or whatever the Default Gateway address is, and pressing Enter on the keyboard.
6. You can attempt to access the router from Internet Explorer by typing 192.168.1.1, or whatever the Default Gateway address is, in the IE address window.  If you can reach the router, a login window will appear wanting your router's username and password.
7. If you cannot ping the router or access it through IE, or if the ipconfig /all doesn't return any valid information, then your computer isn't communicating properly with the router.  The computer and router should be shut down and started back up.  Shut down both, bring up router first, then start the computer to see if it obtains its information from the router.  Complete the above tests again.  If there is still no communication then . . .
   1. The router is bad
   2. The computer's ethernet card is bad
   3. A wire could be bad, check all your connections
   4. Something  in the Windows Operating System networking protocols has gotten corrupt.
8. In all the above instances repairs by a qualified technician are required.