Spam email going to my contacts under my name

I use Microsoft Live email and has gone out to my contacts with emails that appear to come from me but did not nor are they in my sent box.  The is the second time this has happened in a couple months.  I only found out about it because several email were retuned to my mail box because they were either rejected or the email addresses had been changed.  As soon as I found out about it immediately changed my password and ran a complete virus scan on my computer.  I have read the other posts but really does not tell my how to stop this short of closing the account and starting a new one,  can you help??  Please it is very frustrating not to mention embarrassing.