The correct answer is 'Check the BIOS/UEFI settings to ensure the hard drive is detected and the boot order is correct' because the error message suggests that the computer's firmware is unable to locate the operating system's boot files. This is often due to the BIOS/UEFI not detecting the hard drive or the drive not being prioritized in the boot sequence. Checking these settings can often quickly resolve the issue.

Other answers could be potentially correct in troubleshooting 'No OS found' errors, but they do not align with the initial step one should take. For instance, checking the hard drive for corruption with a check disk utility or running an operating system repair utility should only be done after confirming the BIOS/UEFI settings are correct and the hard drive is properly detected.