Page Cannot Be Displayed Errors

Hello. Was hoping someone could help me with this as I'm at my wit's end. I'm having a problem in which some computers can access the Charles Schwab Web site while others can't. More specifically, it's when I try to access the login page that I get the "Page Cannot Be Displayed" error. I've checked security settings, tried adding the site to the Trusted Sites, ran Symantec AV 10.0, even tried running a Winsock repair utility which seemed to help momentarily but not for very long. I've tested this by trying the site from two computers at the same time and so I know it's not the site that's the problem and even compared settings between one computer that can access the site and another that can't seem to. Please help. Thank you.

 

I want to jump on, I have the same problem with various websites. Have to hit refresh, sometimes it works, sometimes it doesn't. What am I doing wrong?