Can’t load most web pages or download from the internet

Please, please, please, help! This started happening out of the blue a week ago. After trying everything I could come up with, I decided it must be a virus so I wiped out my hard drive, reintstalled Windows XP and OMG, it is still doing the same thing! I have ran a hardware diagnostic which turned out A-Okay. I can load comcast.net but not my email. I can load the Mcafee page but can’t download the software. The web pages and downloads act like they are loading but they just get “stuck”. Can anyone help?