Password and E-mail Corrupted

For the second time in a month, the password AND contact e-mail to one of my many blogs have been corrupted.

Can anyone please explain to me why that happens?

Here is the scenario. All of a sudden I go to the WordPress login page for my blog and enter my login and password as usual and get the error message: ERROR: Incorrect password

I go to the retrieve-password-page and enter the e-mail address associated with the account, which gives me the error message: ERROR: There is no user registered with that email address.

1) Are my blogs getting hacked into by someone changing my password and e-mail?

2) How do I prevent that from happening time and again?

A million thanks to anyone who can answer this!

P.S. If anyone can also tell me how the heck to get back into my admin control panel, that would also be kind of nice.