Firefox and IE won't occassionly load popular websites

Hi
I have a very strange problem.
Occasionally websites like cnn.com, msn.com.au, google.com, yahoo etc doesn't load in both firefox and IE. Or websites load absolutely fine eg. whirlpool, businesspectator etc. That after a while could be 30 minutes or so and it will start working again. Restarting the computer does not solve the problem. I have a second computer on the network and that computer is able to excess those websites fine even when the problem computer can't so I guess the issue is specific to this computer in question. I know this sounds very strange and I am at my wits ends trying to solve the problem.

Someone suggested that I change in the MTU in the router to 1500 done that but still no luck.
I tried to ping those websites when it is not loading up it won't go through.
I have discovered if I type in the IP address for google into firefox I can go to the home page but I am unable to navigate any further i.e searches don't go through.
I have run various malware removals:
Superantispyware, adware, anti-malware,combofix, spybot
I have run anitvirus:
trendmicro housecall, avast.
I had macfee security center running initially I have uninstalled but no luck.
I have run TCP optimizer.

Sorry for the long post but could anyone please give tips as to what we can try next.

 

I've only had that problem with a malware. It looks like you are covered in that area. But just to eliminate the possibility of this common malware, if you are on XP Check your startup tab in msconfig and look for a file starting in System32\ with random letters.dll.

 

no luck.. very frustrating

 

I fixed a problem like this last week, unfortunately it was all virus/malware related. Many pages opened Ebay/Amazon etc, but anything with virus, malware or spyware appearing on the pages wouldn't open. links didn't work either

 

Did you use any different malware remover or antivirus compared to me?