There was a major hack of Hotmail accounts around two weeks ago. Somehow someone managed to crack a large batch of user passwords. I had several customers all complaining of the same symptoms over a three day period. You may be suffering from something similar
You need to go online and change the passwords for your account. Also - and this is important - also change the security password reset / recovery questions. If someone has managed to hack your password, they also have the ability to hijack it again once you're reclaimed it - unless you change those security questions
So
1) reset the password to something hard to guess. Either a completely random string, or if your memory is not up to that, then three or more UNRELATED works (e.g. pink BANANA sleeper)
2) make the recovery questions impossible to guess by making the answers unrelated to the question e.g. if you have a question "what your favourite colour", make the answer "reliant robin" or "biggles". Something that no-one who knows you is going to be able to guess