My PC has internet but cant open webpages.

Hi, my dads computer says it has internet connection but wont open webpages in IE or Firefox. I have tried removing loads of programs off it and have taken off viruvirgin media so i brought his computer to my house and it still does the same with my bos/firewall but still not working.
It was working on firefox up until the other day.
I thought it may be a problem with Virgin media he has so i brought the computer to my house and it is still exactly the same even though i have BE Broadband.
The icon on the computer by the clock says it has internet as does the connections.
But it just wont allow me to go on any website. I have tried everything i can think of including removing firefox and IE and re installing them, tried a new virus software, took the computer back to a date before it stopped working and still not working.
I have read loads about this problem and i tried the fix thing someone suggested on it but it comes up with an error message saying some files cannot be found.
I have now downloaded the HighJack this thing onto my laptop and managed to get it onto my pc using a memory card. I will add the report informaton once it has done.
Can anyone please help me this has been doing my head in for days.
BTW im not that good at computers and dont have a good understanding of them just basic knowledge

Thanks

Holly

Please download the current version of HijackThis from HERE

• Double click and run the installer.
  
• It will install to C:\Program Files\Trend Micro\HijackThis\hijackthis.exe
  
• After installing, you should get the user agreement, press accept and Hijack This will run.
  
• Select Do a system scan and save a log file. This will open a notepad file of everything Hijack This found, copy and paste it back here.