My sister in law had the same issue last week. We spent 3+ hours dealing with it, including time on the phone with her ISP, Comcast. Despite doing everything listed in this thread, plus re-registering a bucket of DLL's, no joy.
Later that evening, in casual conversation, her friend who is also on Comcast said they couldn't get into secure sites either.
The upshot: By late that evening, there were reports on dslreports.com that Comcast customers is our region were not getting to SSL sites.
The next morning, Comcast called her back and were preparing to have her revert to a previous system date, or even reload system files. I told her absolutely not, that the problem was on their end.
After some time on hold, they discovered the problem was in their system, and that it had been 'resolved'. Still couldn't get in.
2 hours later, it was back and functioning. By this point she had lost every cookie that she had with all her log ins and passwords, reset all kinds of security settings, etc.
In a nutshell: Could your ISP be the cause?