Safari/OSX having trouble connecting to certain servers?

My MacBook Pro running OSX V10.5.8 and Safari V5.0.3 is having trouble loading certain random pages. Things like verizonwireless.com, rei.com, merrell.com just won't load for some reason, I have had the issue with other pages but these are the most problematic ones. It seems to be pages that are 'flash-intensive' It's like the server does not even register with my computer. The OS doesn't even struggle to access the sites, it just instantly says "no response, cannot load" instantaneously.

Any ideas? I have done some trouble shooting online and deleted some .plists and what not. I didn't really know what I was doing, just how. But I followed the instructions people gave and nothing improved?

HELP WILL BE GREATLY APPRECIATED!!!!!

Thanks guys.