To follow these simple steps to back up of contacts and mails in windows live mail.
Step 1: open Windows live mail and go to FILE Menu
Step 2: then File->Export and select the .pst file(data file) that have your data
Step 3: click next and select the location to save the backup and click next
After format PC install windows live mail and now you can import the back through these steps
Step 1: Start windows live mail and go to file menu
Step 2: File–> import and select the .pst file thet you export
Step 3: Click next and all your data and file will be back in your windows live mail