Try these steps....

Turn off computer. Disconnect router, and modem from power source for 30 seconds. At the same time disconnect signal cable as well.
Power them back on.
Restart computer.

If that doesn't work, bypass router, and connect computer straight to the modem.

If that doesn't work...
Go Start>Run (Start search in Vista), type in:
cmd
Click OK (in Vista, while holding CTRL, and SHIFT, press Enter).

In Command Prompt window, type in following commands, and hit Enter after each one:
ipconfig /flushdns
ipconfig /registerdns
ipconfig /release
ipconfig /renew

Restart computer.

If that doesn't work...
Go Start>Run (Start search in Vista), type in:
cmd
Click OK (in Vista, while holding CTRL, and SHIFT, press Enter).

At Command Prompt, type in:
netsh int ip reset reset.log
Hit Enter.
Type in:
netsh winsock reset catalog
Hit Enter.

Restart computer.


If that doesn't work...
Download, install, and run WinSockFix: http://www.softpedia.com/get/Tweak/N...nSockFix.shtml (doesn't work in Vista)
Restart computer, and check again.

If that doesn't work...
Download Dial-A-Fix (DAF) (doesn't work in Vista):
http://wiki.lunarsoft.net/wiki/Dial-...C_and_articles

Have XP CD available in case DAF needs a file. Likely not!

Check all boxes on the screen (clear any restrictions if it shows any)
Then click GO!

When the entire page is finished click the HammerHead at bottom to go to the second DAF page.

Here, one at a time, do the below:

Reinstall BITS
Reinstall Windows Firewall
Repair Permissions
Reset networking

Watch for any File not found or other errors and make note as this may lead to the fix!

Restart computer.