This is what I would try:
Go to your network connection properties and make sure the following are
installed and enabled:
Microsoft Client for networking
TCP/IP
Select TPC/IP and go to properties, make sure Obtain an IP automatically is
selected.
Exit
Go back to the properties of your network connection and select the Support
tab. If you do not see an IP address click the Repair button.
If the above fails. Go back to TCP/IP properties and select Use the
following IP address:
enter 192.168.1.100
for subnet mask enter 255.255.255.0
Exit and go back to network connection properties and the Support panel. You
should now see the IP address you have assigned. If yes then do the
following:
Go to START, RUN, type in CMD. Then type in ping 127.0.0.1
If the ping is successful then TCP/IP is successfully installed and DHCP IP
assignment is at fault. You didn't mention if you're using a router or
direct connection to the DSL modem. Find out the IP address of the modem and
see if you can ping it.
Other things to try: go to control panel, system. hardware, device manager.
Find the network adapter(s) and see if any problems are reported.
HTH