My email is invalid and I can't log in to any of my accounts?

The yahoo email that i've had for 3 years is suddenly not working and I have no idea why. I cannot log onto it and it says that my password is wrong (I've tried at least 6 different passwords on different occasions and I know that I never changed my password..). The big problem here is that all the accounts I have on other websites (blogging sites, social networking sites, file saving sites), I used that email to sign up with. So now I can't access my accounts on those sites because my email is suddenly non-existent. Help?