Do you have a second user account?
If not, make a new one, and see if your problems clear up in the new account.
It does not matter at this point whether you set the new one as admin or limited user. Mr. Proffitt's suggestion is a known fix or workaround for user account issues such as this one. Sometimes an user account goes glitchy and does not work as it should. Creating a new account should fix that. That is, provided you did try to use another new browser such as Google Chrome, as was suggested at first.
Let us know how you get on. Did it work for you?