Wirelessly posted (8700g: BlackBerry8800/4.2.1 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)
Search your PC for "*.ipd" which is what any backup file will by default end with. They are normally then named by the date of the backup. You will want to find this latest backup file from which to restore.
Further info at the
http://www.blackberryfaq.com/index.php/Main_Page pages.