Some webpages simply never work on my desktop unless I use proxy. Why?

I've been having this issue for as long as I can remember. Certain sites simply never load on my desktop. My Firefox and my IE would indicate that the page is down by returning the following error:

----------------------------------------
Unable to connect

Firefox can't establish a connection to the server at somewebpage.com

The site could be temporarily unavailable or too busy. Try again in a few
moments.
If you are unable to load any pages, check your computer's network
connection.
If your computer or network is protected by a firewall or proxy, make sure
that Firefox is permitted to access the Web.
----------------------------------------


I've got a handful of sites that give this error. I've tried formatting and it doesn't help. Theses same sites work FINE from work, from collage, and from my cellphone (Android 2.3) but NOT my damn desktop.

At first I thought maybe Comcast was blocking them but then I realized that I CAN view them on my Android phone, using Dolphin Browser, or any Android browser for that matter when connected to my Wi-fi which obviously, is the Comcast/Xfinity.

I Google'ed public proxy's and found one called hidemyass which is a web based proxy. I can toss the websites in question into the hidemyass and they work. I've been using the proxy's as a work around but frankly they are SLOW and very inconvenient in general.

I'm lost... Thoughts?

Operating system is Windows 7 Ultimate SP1, 64-bit with all the latest updates.

Wow no one has any thoughts?

Formatting? What type?

Have you tried clearing the cookies and the cache in each browser?