Internet trouble

[Terrorcell]

Ok here's my problem:

I don't know when this started, or how, but sometimes when I'm searching the web using Google and I click on a link to a website I get the following error in firefox:

Unable to connect

Firefox can't establish a connection to the server at download.microsoft.com.

    *   The site could be temporarily unavailable or too busy. Try again in a few
          moments.

    *   If you are unable to load any pages, check your computer's network
          connection.

    *   If your computer or network is protected by a firewall or proxy, make sure
          that Firefox is permitted to access the Web.

And this happens frequently, not with all sites, but even with links that I should be able to connect to. E.g. I tried to download Microsoft Security Essentials Windows Vista 32bit version from the official site

http://www.microsoft.com/security_essentials/default.aspx?mkt=en-us#dlbutton

but i still get that error.

Another annoying example is the Windows Live Messenger games page. With a conversation window open, and after I click on the 'games' button I get:

This program cannot display the webpage

Most likely causes:

     * You are not connected to the internet.

     * The website is encountering problems.

     * There might be a typing error in the address.



Or when I'm trying to update the Windows Security Essentials program, the download bar rests close to halfway, then after a short wait comes up with:

Virus & spyware definitions update failed.

Microsoft Security Essentials wasn't able to check for viruses & spyware definition updates.

Make sure your computer is connected to the internet and try again.

I know for a fact that my computer is connected to the internet as my Windows Live Messenger works, as well as updating the AVG definitions without any problems, or browsing the internet (apart from the already mentioned issues).

I don't know what could be wrong, none of my Ethernet cords are loose and I've run multiple anti-virus and anti-malware checks with no viruses or malware found...

[Khris]

This sounds like a DNS problem.

Whenever you enter a URL into a browser or a program wants to connect to some server, your PC connects to the DNS server to get the IP address associated with the domain name. If that connection fails (because the DNS server is down) or the DNS server's "phone book" is outdated and it sends back the wrong IP address, you end up seeing the message you mentioned.

Go the properties of your internet connection (LAN or WLAN, I assume), then to the TCP/IP properties (IPv4). In the DNS tab, enter these:
208.67.222.222
208.67.220.220

If that doesn't fix your issue, it's very likely a hardware problem.

[Anian]

Oh, I had the problem with browsers as well, basically I couldn't read html (Steam, torrents, MSN etc. worked). Sadly I couldn't solve the problem even after flushing DNS and such. Try Khris' suggestion.

[Terrorcell]

I tried Khris' suggestion, but it didn't work.
That probably means that it's a hardware problem...

[Dataflashsabot]

Also, start->cmd->"ipconfig /flushdns" (without quotes, obv).

[Khris]

When is the last time you have reset your router? Also check the sync speed in the DSL properties/status of the router's menu.

Also, the next time you can't connect to a domain, try tracing it: enter cmd into the start menu's search bar and hit enter.
In the black window, type e.g.

  tracert microsoft.com

This should give you some clue about exactly where the problem is.

(I've once heard a story about a badly configured server at a big ISP and as a result, connections were randomly broken all the time. Some IT guy tried repeatedly to tell the hotline idiots about the problem and that he knew exactly how to fix it, but he had to wait two or three days until the provider fixed the server because they wouldn't listen.)

[Terrorcell]

I managed to fix the issue by reverting to a week old restore point. All other attempts failed though.
Thanks anyway