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Everything was working perfectly a few days ago. However, now I can't visit e.g. some .edu sites or Ebay - they time out. I tried to download AVG but it wouldn't start the download. Several other big name websites also don't work. Google works fine, this site too.

In my hosts file, everything is # commented. The last two lines are as follows:

# localhost name resolution is handled within DNS itself.
#       localhost
#   ::1             localhost

I tried to ping Ebay and a .edu site. Both timed out. Google and a few others worked fine.

Turns out it was with the provider. Thanks for the help everyone.

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Can you ping the sites that work and the sites that don't and see if there is a difference. Also, check the file c:\windows\system32\drivers\etc\hosts - it should only contain localhost. – Paul Apr 17 '12 at 5:02
Updated main post* – Meowbits Apr 17 '12 at 5:08
Ebay doesn't necessarily respond to pings, so you'll need to confirm it on a machine that isn't having problems. Once you identify one, do a tracert rather than a ping. This will show where the site is getting blocked. – Paul Apr 17 '12 at 5:14
everything in the sample you provided is also commented out, your problem is somewhere else. – Toby Allen Apr 17 '12 at 6:35
If you found the answer to your own question, post it as an answer and accept it so that we don't see this as unsolved. – bwDraco Apr 23 '12 at 0:37

There are many different possibilities as to what's going wrong with your connection; it could be at various levels, including:

  • Your browser (try a different one, install one downloaded from another machine if necessary)
  • Your proxy settings (try bypassing proxies - ok, probably an unlikely scenario for your parents' connection)
  • Your firewall settings (try turning off firewalls to see if it makes a difference)
  • Your network card (i.e. at the hardware level; try a different machine on the same network)
  • Your modem/router (which may have its own firewall/filtering settings etc. - look for log files or look through the settings to see if anything may have been modified)

Other possibilities are that you indeed have a virus (since that's what you tagged your question with), so a scan with anti-virus software would help (download with another machine if necessary), or that you're just plain unlucky and happened to test sites at the exact moment that they were down (rather unlikely...).

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  1. Open up a command prompt (Start > Run > "cmd.exe" > OK).

  2. Type in the command ipconfig /flushdns

See if you can connect then.

If not, contact your ISP and ask whether their DNS servers are having trouble.

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Many things can cause this. A systematic approach to troubleshooting works best, coupled with insight.

I'm guessing your network setup is one computer that connects to an ADSL modem over ethernet or wifi. You might want to elaborate on this.

  1. Try power cycling (restarting by removing the power for about 10 seconds) your modem (assuming you use ADSL or cable), then restart the computer.

  2. Check you're not running a program that is saturating your connection (e.g. bit torrent). At a command prompt, running netstat can give you some insight into what your computer is talking to.

  3. Check no-one else is using the network while you troubleshoot, either plugged in via ethernet cable or over wifi (and it's a good time to check you've got a wifi password).

  4. At a command prompt, run nslookup to see if it will resolve the URL to an IP address. It should do it reliably, as you can reach this site.

  5. Check with your ISP that you have not been "shaped" for going over quota.

  6. If you have a Linux live cd you could try booting it to narrow down if the problem is with Windows or the network. (Generally a restart of the modem sorts out network problems if you haven't changed any settings in it recently.)

  7. If Linux works fine, you know it's something to do with the Windows install. It could be a restrictive firewall, although if it was working before and then stopped without you doing anything it may well be malware/viruses etc.

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In a specific case when I helped someone with the error description "some sites don't work, others do", I managed to extract that all https connections were refused, and since some sites automatically redirect to https, these sites did not work at all.

If you find that this is your problem, and you use Windows, either google for the problem or ask a new more specific question here on SU. There are apparently many things that can go wrong in a Windows installation with this consequence, and I personally ran through the entire error searching process in the Microsoft Knowledge base article on "You cannot log in to or connect to secured Web sites in Internet Explorer" (it was not restricted to Internet Explorer, though) before resorting to a reinstall of the OS.

This can also happen on the router side, so before doing the above, at least restart the router and see if it helps.

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