can't send yahoo email & security certificate


New Email
Well, I can log into my email, I can view email already received but when I write an email and hit send, the program closes. Also, often when I try to log in I get a pink screen that says something about a security certificate.
I don't log in when I get this but I did once. Since then I changed my password. I appreciate any help you can give me as yahoo is impossible to get to. Thanks.