I was having simular problems with a couple of other web sites - I cleared out history and cache several times, and tried all sorts of internet options with no luck.
It turned out that there was a VIRUS - on the University SERVER - NOT my computer - that was blocking certain web sites to all faculty and student computers on campus!
One of the sites was my BANK. As the bank is in TEXAS, and I am in IOWA, I rely on the 'net to manage my accounts. So not being able to get to that website was a big problem!
Once our Informational Tech folk cleared that up, I could again get the web sites!
So you might check with your ISP !!!
Good luck!