Some website are unaccessible

How can it be possible that you can access a website and others don't, just out of blue?

I had my PC connected all day yesterday and all last night.  This morning, 6am, I goto my notebook (nobody has been in the office since 530pm yesterday and I was the last one to leave 11pm), and I can't connect to some site, yet I can connect, upto now, to aol.com  (and obviously http://www.experts-exchange.com).

I can't connect to google.com, yahoo.com, microsoft, etc.  the only one I seem to connect with no problem  is aol.com (and obviously http://www.experts-exchange.com)

We use DSL and also I can connect to DEL provider site.

There has been no changed to firewall, I haven't installed anything, etc (only yesterday morning I installed in my notebook Internet Explorer 8); I use Internet Explorer and Firefox, both same behavior.

How can this be? How can it be fixed?

(Note: I haven't resetted the modem because this has happened before and would like to diagnose the problem)
rayluvsAsked:
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
  • DNS may not work. Try to use nslookup www.dell.com for a test.
  • DNS Cache service killed. Have a look into your services for it, start/restart it, and try again.
  • Malicious software, faking DNS, manipulating hosts file etc. Have a look into %SystemRoot%\system32\drivers\etc\hosts, if there are entries for the websites you can't access.
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JohnBusiness Consultant (Owner)Commented:
One possibility is malware. Go here to see if this page comes up properly:

http://www.confickerworkinggroup.org/infection_test/cfeyechart.html

If not, you could have a virus. ... Thinkpads_User
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rayluvsAuthor Commented:
Ok, I should've include also, that I have 7 PC in the Lan.

Only the server and my notebook has been on.

My notebook has Comodo firewall, Spyguard, Spyblaster, Spy-bot teatimer, AVG Antivirus and Adware, all resident and online.

I turned on one of the computer that has been off all night and same result.  I have an iphone and I have internet included.  My iphone internet connection work fine and can goto the sites I can't in my Lan, but when I connect wireless (Lan( with the iphone, same result.  So its something here.

By the way, I can't connect to the link you sent.

(this is super crazy)
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
Sounds like the central DNS server config is failing. Please try
nslookup -d2 -v www.dell.de
nslookup -d2 -v www.experts-exchange.com
and compare the results, in particular the servers asked.
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rayluvsAuthor Commented:
Ok...here are the results attached

The IP  172.16.0.1  is my DSL modem.  I can ping it and goto into it.

Result-1--DELL.txt
Result-1--EXPERT-EXCHANGE.txt
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
The DNS server seems not work in your DSL modem. Reboot it, if you do not know better. I suppose your iPhone is using fixed DNS server from outside instead of the modem, and that is why it works, but not with WLAN where it will use the same settings as all PCs.
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rayluvsAuthor Commented:
Ok....will do.

But why does this happens?
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rayluvsAuthor Commented:
How can  prevent this?
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rayluvsAuthor Commented:
Just got everything working and didn't  have to reset modem; I don't now how it got fix.

So basically, I would like to know:

But why does this happens?

How can  prevent this?

Thanx
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QlemoBatchelor, Developer and EE Topic AdvisorCommented:
It might be a bug in the modem firmware so it's loosing its DNS server info, and/or the modem did not negotiate DNS server info with your ISP after reconnect, or it was (tried to) hack the modem, leading to a internal crash or blocking of DNS.
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