So long as you have all the drivers - you could try removing the network adapter then run detect new / changed hardware and it should see the adapter and re-install it. This approach can help when part of the software layer of the IP stack has been corrupted as it will refresh it.
As said above - from a DOS window run the command
ipconfig /all
report what is seen - does it have a valid IP address, IP gateway and DNS servers listed?
Net try
ping
www.google.com.au
Did any / all pings make it - without more diagnostic information can only give you limited advice.
Matt