It might be a problem with the DHCP of the router, that it's not assigning ip's correctly.
Step 1) Try rebooting the router.
Step 2) Try to ping the router's ip, if successfull, try to ping 216.239.57.99 (that is google), if successfull, ping google.com
Step3) type the command (Ipconfig/ all) in to your commandline, check if you get ip
Step4) run Spybot or Adaware to clean out any possible spyware that could be killing your bandwith.
http://www.lavasoftusa.com/
PS: Let me know if your network card is pulling an IP address, and if it starts with 169.254.