Computer can't boot to either OS (dual boot)

I have 2 OS on 2 separate HDD: Windows 10 and 7. Yesteday I wasn't able to boot into Windows 10 anymore as it said something not bootable. Windows 7 still worked .

I tried doing bootrec /buildbcd, /fixmbr, /fixboot and /scanos but same issue. It does detect there is 2 windows OS tho.

I then tried this website: How to repair Master Boot Record (MBR) on Windows 10 - Pureinfotech

And I did this command:

BCDedit /export d:\BCD_Backup
D:
CD boot
Attrib BCD -s -h -r
Ren d:\boot\bcd bcd.old
Bootrec /RebuildBcd

And now even my Windows 7 doesn't work. Both OS shows a light blue screen with no words and reboots.


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I fixed my Windows 7 portion via Startup Repair from my bootable windows 10 USB. But i'm still having trouble with Windows 10; computer doesn't detect it anymore.


I tried doing bootrec /buildbcd, /fixmbr, /fixboot and /scanos but same issue. see pictures

So my Windows 10 got fixed by itself it seems. I went into cmd again to do some bootrec commands again, didnt work. But after i exited cmd, i saw an option to load another OS, and then i saw my windows 10!





this wasn't here before.

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SIW2 said:

Can't see those pics directly. Can you post them here on the thread?

Were you using the system partition on one disk to boot both os?

will reupload. seems to be allowing me now.

To answer your question, im not sure. i've always installed the OS on separate physical drives. Right now at least, the boot priority has to be on the Windows 7 drive first, or else both OS wont show up.

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On my windows 10 portion, I can't see my Windows 7 partition drive when I go into This PC. I see it in disk management, but its not label. in Disk Management, i see a large partition that's unlabeled (seems like my windows 7), Can i fix this by changing the drive letter/path? (UPDDATE: yes it does it seems).




Funny thing, In windows 7, everything seems fine:

Although you have Win 7 and win 10 on two separate drives, you haven't disconnected (SATA or power cable) on the win 7 when installing Win 10 so it installed the boot manager under drive 1 System Reserved partition.
You made so many modifications with bootrec that the active partition is now on C: (and it should be System Reserved).

You have so many partition on drive 0
Please open a CMD as administrator and type:
diskpart
sel disk 0
list part
sel disk 1
list part
exit

Post the results of list part of drive 0 and 1 here.

Siw2 can help you better than me. Follow his instructions

He has a 4tb disk with win10 label on the first partition.

The other disk is 1tb and has the win7 os partition marked as active, system.

We shall assume those are both mechanical disks ( unles the op says otherwise)

They both appear to be mbr partition style.

He would be better using gpt on the 4tb disk.

if his bios supports both efi and bios boot: convert the 4tb from mbr to gpt, and use the system partition (esp) on the gpt 4tb to boot both os. Because in my experience, the efi bootmanager is able to work with with winload.exe. That way the 1tb disk with win7 could remain as it is and doesn't need conversion.

That assumes his bios can boot both modes. But I am not sure it does if he is using Core 2 Quad Q8400.

The problem here is he can't acces the full 4tb unless he uses gpt partition style on that disk.
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I would rather have both os on an ssd and use mechanical disks only for storage. Unfortunately the 120gb sdd pictured is too small for that.

I think the best solution is to get a 500gb + ssd , run both os on there in bios mode ( because doubtful his bios supports both boot modes ) .

Then the two will os work noticeably more quickly ( even if it only a sata2 connection ) , and he can use the mechanical disks as storage with the 4tb converted to gpt so he can utilize all the space on it.

That is what I would do. But making those changes is a bit complicated for somebody who is not familiar with this kind of thing.

If he leaves it as is, he should be able to continue to boot both os in bios mode on those slow mechanical disks, but he can't acess all that space on the 4tb disk. So it is a waste.

EDIT:

Alternatively, transfer the win 10 to the same 1tb disk as Win7. Then convert the 4tb to gpt to use as storage. That way doesn't require buying an ssd, but then he wouldn't get the benefits running the os off an ssd.

On my windows 10 portion, I can't see my Windows 7 partition drive when I go into This PC.

Thats because the win7 partition is the partition from which win10 is started up.

The boot manager is on the win 7 partition, he reaches over to the win 10 partition to start it up.

The partition where the bootmanager ( and related boot critical files ) lives is called "system" by microsoft.

Windows like to hide the "system" partition from the end user by not automatically allocating a drive letter.

So you dont see it in explorer when booted into win10.

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The partition containing bootmgr and his relatives is called "system".

The partition containing the operating system that has been booted up is is called "boot".


Often "system" and "boot" are different partitions, and can be on different disks.

It also possible to have "system" and "boot" on the same partition.

When "system" and "boot" are on the same partition, Windows does not hide it from you.

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The usual scenario for win 7 is a small 100mb fat32 formatted "system" partition and a separate larger ntfs formatted partition for the win7 os.

For bios boot the disk is mbr partition style and the 100mb is marked active.

It is similare layout for win7 efi boot, except the disk will ( usually ) be gpt partition style.

Those are the usual/default layouts. However depending on your bios capabilities, you could have different layouts.

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My Windows 10 is SSD. back then I believe I chose MBR instead of GBT due to compatibility reason

How can I make my Windows 10 independent from my Windows 7?

boot into windows 10

Assuming your win10 osletter is c: when you are booted into it

EITHER:

Open an administrator cmd prompt and type :

diskpart
sel vol c
act
exi
bcdboot c:\windows /s c:

press enter after each command above

OR:

you could use disk management to mark the win10 partition active ( open diskmgmt, rt click the win10 partition, select mark as active from the context menu ).
then the admininstrator cmd only for bcdboot
bcdboot c:\windows /s c:
press enter
you should get success message.

Then you can boot directly into win10 if the win7 disk is unplugged, or if win10 disk is first hd in bios boot order.