Depends how your password was set, if it was all letters or a name or a place etc a brute force password hacker could do it easily with enough time, he/ she also could have went via your secret clue etc to get into it, or its someone you know but dont realise it, (( and dont say anyone you know wouldnt do that happens all the time )) Yahoo i very much doubt will do anything at all to help.
If you do use things like online banking etc and you send the info to yahoo, well thats just stupid, all info like that should go to an ISP email, like verizon etc, that is accessed from outlook or another email program, it offers far better security,
Have you tried the secret question and answer to see if that still works, also how did this person contact you to ask for money after they took the account???
neither have I. But take that firewall away and see how many connections are attempted against your machine.
They dont try to connect to your machine, my firewall records it all, even when off, people dont aim for your system, your not the special 1 in the world there after, most people are too dumb when it comes to the net, and dont pay attention to the signs, esp the ones who download things they dont know what they are, or who there from, the scans on your system are just random port scans, that people are running in a range of IP's, websites even do this, thats why certain websites look like there trying to hack you,
I personally wouldnt run 2 firewalls, 1 is enough, and no firewall is secure unless it blocks the ports that these people are looking for.
If you create another account make the password L37T3R5 and numbers, as a password maker cannot create these so easliy or the person doing it may not want to make them due to the massive number of passwords it would have to create in order to make a match. Remember the most common password is someones name, or place they live, cause jeez no one would ever think of those.