To turn Secure Boot on, follow these steps:

1. Check if Secure Boot is already enabled by typing "System Information" in the Windows search bar, opening it, and scrolling to "Secure Boot State." If it says "Off," proceed to enable it.
2. Open Windows Settings by clicking the Start button and selecting "Settings."
3. Go to "Update & Security," then select "Recovery" on the left sidebar.
4. Under "Advanced startup," click "Restart now."
5. After the PC restarts to the "Choose an option" screen, select "Troubleshoot," then "Advanced options," and then "UEFI Firmware Settings." Click "Restart."
6. In the BIOS/UEFI settings, navigate to the "Boot" tab and ensure that the Compatibility Support Module (CSM) is disabled (set "Launch CSM" to Disabled) to enable UEFI mode.
7. Find the Secure Boot option and set it to "Enabled." Also, set "OS type" to "Windows UEFI mode" and "Secure Boot mode" to "Standard."
8. Save changes and exit the BIOS/UEFI (usually F10 to save and reboot).
9. After Windows boots, verify that Secure Boot is enabled by checking the "Secure Boot State" again in the System Information.

Note: If your system disk uses MBR partition style instead of GPT, or if BIOS is in legacy mode, you may need to convert to GPT and enable UEFI mode first. Also, BIOS menus differ by manufacturer, so instructions may vary slightly depending on your PC model.