basically reinstall xampp, and upload your backup database, if you have made a backup as you say you have, then you shouldnt think twice about reinstalling xampp
Ah , I suggest you get IIS , and how someone hack into your db , unless you did'nt put security up , or maybe you put ur password so easy , MAKE YOUR PASSWORD HARD.
or someone placed a keylogger on your computer.
Simple, in xampp go to mysql\data your database will be there, drag the folder to the desktop, when you re-install xampp, drag it back into the mysql/data folder.