I can't come in my yahoo accounts today. I have 3 accounts, 1 works correct, but 2 other show the error in my passwords today. I've just created new account, but it shows that error too. I deleted cookies, not helped. Who can say what this mean?
May be worthwhile running a spyware scan. For all you know, some malware may have hijacked your machine.
I suggest you wait for a while, then try again, if you still can't login, then try contacting yahoo support.