In my Dell Inspiron laptop, the key is F12 to bring up the boot menu for selecting a boot media or entering into BIOS. If you can’t see your attached USB flash drive, you need to enter into BIOS: disable Secure Boot Control and disable UEFI boot mode.
Regards to password reset, you can use Windows installation disc & sticky keys trick:
http://www.top-password.com/blog/reset-windows-10-password-with-sticky-keys/
This security hole exists since Windows Vista, and it’s not fixed now.
