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I had a dual-boot setup of Ubuntu 13.10 and Windows 8 on my Asus Vivobook. Initially the dual-boot setup asked for some tweaking as Windows 8 insisted on being UEFI started. But it worked lateron.

This morning, I was silly to accept the proposed upgrade to Windows 8.1. Now windows has replaced the boot manager and I no longer get asked if I want to boot to Ubuntu. The computer boots straight to Windows.

As I really require both OS's, I have been trying to create a functional dual boot situation. I partly succeeded, but for the time being, I am stuck in a situation where the Grub options are shown, and only Ubuntu can be started.

Whenever I try any of the Windows booting methods provided in the grub menu, I get a nice blue screen with the message:

Your PC needs to be repaired
Error code 0xc0000225

After Return, next nice blue screen says:

File:<Windows<system32<winload.efi is missing with same error code.

I have CSM enabled in BIOS, as well as "secure boot" option.

So, how do I reinstate dualboot after upgrading to Windows 8.1?

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possible duplicate of Windows 8 removes Grub as default boot manager Yours is basically a special-case of the referred-to question, but the same solution should work. – Rod Smith Dec 9 '13 at 22:48
This is a duplicate to… – jquerynewbie Jan 11 '14 at 18:53

You need to fix the windows bootloader.So boot windows installation disk then click on the Repair your computer option at the startup.

After that click on the command-prompt option.In that command-prompt run the following commands to fix the windows bootloader,

bootrec /fixmbr
bootrec /fixboot
bootrec /rebuildbcd

And then try boot-repair.

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You can use boot repair to fix boot issues.

It should get things sorted out for you.

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