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First of all, I know a lot of people has asked this question, but after revising a lot of questions, I didn't find my answer so I ask here because I'm desesperated and I need a solution... Here's my problem:

I have Windows 8.1 preinstalled in my PC, and I've also installed Ubuntu 12.04. Firstly, when I installed it, it worked perfectly and I didn't have any problem running the two OS.
But, lately, this last week, it gave me some errors because I couldn't start Ubuntu, so I reinstalled it. The problem now is that when I try to access my Windows 8.1, it gives me this error:

Error: no boot disk has been detected or the disk has failed.

When I enter my BIOS settings, it successfully shows the Windows Boot Manager under the boot menu options, but when I try to access it, it gives me that error. Also, I've tried to solve the problem with the Windows 8 recovery mode but it doesn't detect my OS... I know my hard drive is working, because I can access to my Ubuntu and I can also access my Windows 8 files through Ubuntu.

I've found this guide but I'm not sure if it's what I have to do, is it? If this could solve my problem, I'm stucked in the first step where I have to assign my EFI partition a drive letter, because I don't know which volume is my EFI partition. Here is a view of what I see in my recovery console

So, I would appreciate it a lot if you could help me because I really need to access my Windows 8.1 without losing any data...

share|improve this question
Have you tried the "startup repair" option in the Win8 recovery? Most likely only Windows 8 will show up after that, so I would use EasyBCD to add Linux to the list afterwards. Also please clarify what you actually want to do in your question. Do you want to have a running Windows installation? Linux only? Impossible for us to know, having "access to your Windows 8.1" isn't clear, do you want to boot it or salvage data from it? Also see… – pzkpfw Mar 15 '14 at 17:55
@bigbadonk420 Oh, sorry for not being clare. What I want is to have accessible my Windows 8 via the Ubuntu GRUB menu, like it has been always working. Btw, two or three months ago, I tried to use easyBCD but I couldn't access Ubuntu via that menu. Now my problem is that I can't access Windows 8, so I want to repair the Windows boot menu so it lets me access either my Ubuntu or my Windows. – peregraum Mar 15 '14 at 18:04
So did you try "Startup repair" or not? That should give you a working Win8 boot menu, and adding Ubuntu from there should be trivial with EasyBCD. Your other option is booting Ubuntu from USB and reinstalling GRUB if you want to use that:… -- for dual boot I usually prefer just modding the Windows boot screen – pzkpfw Mar 15 '14 at 18:06
@bigbadonk420 Yes, I tried startup repair, the automatic one. But when I try it, it asks me for a OS to boot from, but I have no systems in that list. Also, my Ubuntu is recently installed, because I reinstalled it one or two days ago. The problem is for my Windows... When I try to boot to it, it gives me the error: boot disk not detected or the disk has failed. – peregraum Mar 15 '14 at 18:13
So you're actually getting a GRUB screen just fine, but choosing the Windows option there gives you the error message? – pzkpfw Mar 15 '14 at 18:15

Follow this`Ubuntu community page for your problem. It can surely helps you in a long way.And if any problems occurs after these steps please comment below .

share|improve this answer
Oh, thanks! So with this I can assume that Windows is installed in EFI mode and I'll have to reinstall Ubuntu in EFI mode too, am I right? – peregraum Mar 16 '14 at 12:06
Does you run the boot-repair as mentioned in community wiki,As far as my experience says you don't have to reinstall the Ubuntu. – ankeet_ Mar 16 '14 at 13:01
Okay, I've done what the guide (the one I put in the main post) said, and now I can boot into Windows. But the problem now is that the Windows 8 option in the GRUB menu doesn't work. So, do I have to use now the Ubuntu boot-repair to change that setting in GRUB, like you said? – peregraum Mar 16 '14 at 13:33
Yes , try the boot-repair and click on recommend setup. After the repair it generates a log file and a customized detail URL , save it, if in-case any problem occurs. This can surely helps you.As you previously mentioned you can also check whether secure boot option is turned off or not. – ankeet_ Mar 16 '14 at 16:35

Maybe you can look via Gparted how big your EFI-partition is and then identify it simply by the size.

share|improve this answer
Oh, thanks for answering! Here is a screenshot of my GParted, where I can see that the efi partition is the one with 360MB, so it should be the Volume 6 partition, am I right? – peregraum Mar 15 '14 at 17:54
This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. – precise Mar 15 '14 at 18:49

When your system boots up hit f12 repeatedly a few times to get an os selection menu. Select windows 8 boot manager there and hit return key. Your windows 8 os should start normally. Worked for me.

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