There is no way to create a backup of your data from Bluestacks if you can't open the program. To fix your problem, you can try to unsintall the application by going to Start > Control Panel > Add or Remove Programs (Windows XP) or Programs and Features (Windows 7). Select Bluestacks and press Uninstall. After you did this, try to open My Computer, right click on the drive on which the program was installed (its default location is C:) choose Properties > Tools tab and perform a Disk Check. Also, before you download and install the latest version of Bluestacks from the official website, use MalwareBytes to perform a full scan of your system.