obviously the first thing you should do is backup your system now - lest anything else you do exacerbates the issue
I'd read this
https://dev.mysql.com/doc/refman/5.1/en/windows-installation-layout.html[
^] and see if you can find any of the data files, OR, do a disk search for my.ini and have a look at that - iirc that file outlines where the data is stored... once you can ascertain if the data is there somewhere you can go on - this has a few hints on recovering for ISAM and InnoDB files, different OS, technique should be the same
http://stackoverflow.com/questions/484750/restoring-mysql-database-from-physical-files[
^]
Im guessing you dont have a restore point or backup before you re-installed the OS ?
Did you install the OS into the same location as the original ?