The error Operating System Loader has no Signature pops up because of a bad boot image file that is not being identified by your system. It would be very troubling as it pops up on boot up and therefore, stops you from gaining access to your files. Here we will let you know the process through which you can fix this issue.
1) Doing a hard reset: On a PC you can do it by switching it off and delete all the peripherals. After deleting the power cable and tap and hold down the power button for half a minute. You will see that it will hard reset your system to the factory default settings. In case of laptop, you can do it by switching it off and deleting the AC cable and the battery. Then press and hold down the power button for half a minute and your laptop would perform a hard reset.
2) Resetting BIOS:
i). As first step switch off your system, power it on and tap F2 for a few times.
ii). You would be in the BIOS settings where you can scroll to the bottom and see the option named Restore Settings or BIOS Defaults. Just tap that. For more info open up https://appuals.com/fix-operating-system-loader-has-no-signature/
3) Changing the boot sequence:
i). As the first step open the BIOS setting and choose the option named Legacy mode.
ii). In case it doesn’t fix this error then you can turn off the option of Secure Boot.