This is a very old problem with a LOT of causes, but sometimes its something simple that can fix it. First, make sure its not just you! Try http://isitup.org/ and see if they report a site to be down. But, sometimes the site is just fine, and only the computer you’re using can’t see it.
For those situations, more work is needed. First, power cycle the modem and router you’re using. Power them both off. Wait 5 solid minutes. Power the modem back on, wait until its completely online and then power up the router. Wait 1-2 more minutes. See if you can browse now. No? Do not despair!
You might need to change a setting called MTU. Its not super easy to change, but its pretty simple. This fix applies to Windows Vista, 7, and 8. XP is a bit different and I’m not going to cover it here.
1) Open an Administrator command prompt
Vista/7: Click Start, then type “cmd” and then right click on it and “Run as Administrator”
Windows 8: http://www.eightforums.com/tutorials/2754-elevated-command-prompt-open-windows-8-a.html
2) Type in this command. You can copy/paste it if you want to:
netsh interface ipv4 show subinterfaces
You will see this:
There you can see all the interfaces that we can change the MTU on. The one in use will be fairly obvious. On the one above, the “Wireless Network Connection” has the most Bytes in/out and is surely the one we want to target. You can also see that the MTU is 1500. That’s the maximum, and its default. Its fine.
Now we’re going to change it.
3) You’ll need to modify the following command. Instead of “Local Area Connection” you need to make it have the name of the interface you want changed. If “Local Area Connection” is what you want changed (it very well might be) then you can leave it.
netsh interface ipv4 set subinterface “Local Area Connection” mtu=1492 store=persistent
Make sure that the name of the interface is in quotes as shown, and paste it in. Then, repeat the command in step 2 so you can see your change as I’ve done here for demonstration purposes:
There it is, clear as day: Local Area Connection’s MTU is now 1492. See if that doesn’t fix your problem. It might, but it might not. There are a LOT of things that can go wrong. This is just one of them, and this is a quick and easy fix. If it doesn’t work, just move on to something else.