This is difficult to troubleshoot as all inconsistent problems are.
Our first suggestion is to verify that you can access other sites.
Second, try to clear your browser cache. Sometimes computers load an old version of a page they saved on an earlier visit; this should clear it up.
Third, and I know it seems like it shouldn’t matter, reboot your computer. It’s been too many times that I refused to reboot thinking, “It’s the web, it can’t be my computer!” only to discover that rebooting fixed it.
If none of those ideas work, drop us a line.