I had the same problem for a couple of weeks - looked through loads and loads of articles and read lots of technical info - most of it useless. My fix, in the end was simple, my Malwarebytes Anti-Malware program had 'Website Blocking' checked. Unchecked and voila, everything back to normal. So simple that I never even thought to look at it. If you have a program like this then check it.
well tis just no firefox, or ie, or chrome, ive even tried downloading opera and still doesn;t work, I am also the administrator of my computer. and proxies seem to work o.o I was able to access both sites using one.