This happened to me after I upgraded yahoo - EVERY time i went to log in i had to go through all the security protocol  chandging passwords etc and i could not go in past the log in page --- what i had to do each time i wanted to go into yahoo was; go to tools, internet options, delete cookies (general tab) it worked for me i had to do it a few times when i went into yahoo but its fine now - its very frustrating try it it should work for you   CathC