Just to be on the safe side I would run a spyware scanner, a virus scanner, clear cache, clear my recycle bin and defrag the computer. Chances of any of this being your issue is negated strongly by the same problem appearing on your son's machine, but at least your machine will be cleaned up, checked and probably operating at least a little faster.
And no, I have not heard of that kind of problem.
1) If you had not been able to get in at the library I would assume it was your password--your password is obviously fine.
2) Others were not experiencing a similar problem so it is safe to assume it was not a site problem.
3) That the problem existed with both machines at your house would indicate it is not a machine specific issue.
I am assuming that neither you nor anyone in your house has changed your firewall settings so that you are effectively blocked from the sites.
The only piece of the puzzle left is your ISP and that is unlikely as well since you were able to get as far as the sign in page (except that the machine may have been pulling that up from cache). Thus the suggestion you clean up your machine and if you still cannot get to the site (and can't even pull it up now to the sign in page from cache since you cleared that), you need to spend some quality time on the phone with your ISP.