Hi Thompson,
1. Is your computer connected to domain network?
2. Do you remember making any changes on the computer prior to the issue?
3. Are you able to access the website from another (third-party) web browser?
4. Are you using any proxy server?
You may face this issue if the website admin has blocked your computer IP from accessing their website. I would suggest you to contact their Support Site. If your computer is connected to domain get in touch with your computer admin.
You can follow the suggestion from this KB article and check if it helps:
Cannot access some websites in Internet Explorer
http://support.microsoft.com/kb/967897
Disclaimer: The Reset Internet Explorer Settings feature might reset security settings or privacy settings that you added to the list of Trusted Sites. The Reset Internet Explorer Settings feature might also reset parental control settings. We recommend that you note these sites before you use the Reset Internet Explorer Settings feature. Resetting Internet Explorer isn't reversible, and all previous settings are lost after reset.
Hope this helps. If you need further assistance with Windows, let us know and will be glad to help.