If I read http://www.howtogeek.com/186881/hard-disk-passwords-explained-should-you-set-one-to-secure-your-files/ right, it's stored on the hard disk itself. So replacing the hard disk and reinstalling Windows should solve the problem.
I just bought the Toshiba Satellite C55D-C5271 laptop pre-installed with Windows 10 and wanted to reformat the operating system back to Windows 7. Carelessly, I set a password to HDD and now, every time I boot my laptop, the HDD password box shows up. No changes take place when loading the default. Resetting to factory settings does not help. Pressing (0) and then, Power Button only freezes the HDD password box. When I do get access to BIOS settings, the HDD password section can not be changed. I have searched through Youtube for help and most of them show take the laptop apart. Hopefully someone can help me.

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