Quite a few ISPs use Yahoo as their mail provider - here in the UK, BT is one such. This could be a simple explanation of part of the problem. Because the account has been compromised, maybe it has been blocked.
There has been a spate of fake emails with 'video attachments' or some such which then cause the user's email account to be compromised. This would typically happen when the attachment is opened whilst logged in to webmail.
Usually you can sort it out fairly easily - on the log-in page you should find a link for changing your password. Only do this after running a security scan (not just ant-virus) on your computer first.
After you've changed your password you will probably find the mail provider asks you to do it again, because they have detected suspicious activity on your account.
However, if the account has been blocked you may have to contact the service provider for advice.