I re-installed Windows on my ASUS X453s laptop using usb thumb stick, but the PC won't boot into the thumb drive to initiate installation, there is simply no option to use device on Windows 10 Advanced Startup. Based on the question and the answer here, I disabled the Secure Boot Option, and enabled Launch CSM, restarted PC, hold the ESC key, select USB drive and installed Windows 10 without any problem.

However, after installing, I reverted the BIOS setting to default, which enabled Secure Boot Option and disabled Launch CSM, then after a restart, the PC boot straight into BIOS, without Windows Boot Manager available on the boot option (it was there before re-installation). If I disabled Secure Boot Option and enabled Launch CSM again, PC boot into Windows just fine, and there are two option to boot in BIOS, #1 CD drive, #2 Hard disk, but there is still no Windows Boot Manager available.

How do I rectify this?

Since before re-installation PC will boot into Windows even if Secure Boot is enabled. I think I need to add Windows Boot Manager manually, but there is no "add a new boot option", only "delete boot option" is available.

If my assumption is correct (this is my first UEFI machine!), I re-installed the new Windows as non-UEFI OS, that's why I can't boot into it with Secure Boot enabled, but I can't figure out a way to install it without disabling Secure Boot. The Windows used is

  • The fact you enabled CSM tells me your using MBR partition. So disable Secure Boot or convert to GPT – Ramhound Sep 10 '16 at 3:36
  • "I re-installed the new Windows as non-UEFI OS, that's why I can't boot into it with Secure Boot enabled," - because you installed in legacy mode installed of UEFI mode, Secure Boot only works, if you install the OS in UEFI mode. – Ramhound Sep 10 '16 at 3:37
  • Thanks, I'll try to boot the USB drive in UEFI mode but I still can't figured out how, the thing is if I booted Ubuntu using the same thumb drive, it boot even in UEFI mode. Is it possible that the Windows installation I used doesn't support UEFI? It's Windows 10 ISO straight from microsoft server, and I created it using Rufus. – Nur Sep 10 '16 at 3:43
  • Windows 10 supports UEFI mode. Tell us what settings you used with Rufus, if they are not correct, then its not a valid EFI device. You have to disable CSM, and you can either enable or disable Secure Boot, Secure Boot is 100% optional – Ramhound Sep 10 '16 at 3:46
  • As a note - UEFI can only boot flash drives formatted in Fat32. Like Ramhound says, you should be able to select UEFI with secure boot off. – Randy Schuman Sep 10 '16 at 4:08

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