Check email configuration, no way to tell how you had it setup or what exactly happened. When you said "re-booting" do you really mean "re-booting" or "re-installing" or "re-imaging"? Many non-computer people like to say reboot when they actually mean reinstall.
If you re-installed Windows you probably had a .pst file in your old user profile, if you did not save it, need to run a file recovery program like Recuva to see if it will find it. Then just configure Outlook to open that file.