Hi Serena,
Changing your password and security questions is always a good first step.
The fact that your password still worked and you were able to change it is a good sign.
If you post the
full email headers from one of the sent emails from last night we can help you figure out if it was sent from your cmputer or not, and if not where it was sent from.
As for the missing emails that used to exist, if they are missing from your Hotmail account you will not be able to retrieve them. Hotmail's public community support doesn't seem to exist anymore so while we can help you with reading the email headers and fixing problem #1 we can't fix #2 the server side problem related to restoring emails to your account on the Hotmail servers.
-Raymond