Hi all, so I recently set up dual booting on seperate drives so that I could play a few games that have that pesky agressive anti-cheat, while still having my beautiful beautiful endeavouros setup. Now, after a series of unfortunate events of partition changing (i have a poor history with this), I had to reinstall… again, but luckily windows should still be intact on the second drive. Now, theres no boot manager for windows so I can’t access it. I’ve tried finding resources on how to recover a windows boot manager, and I’d really like to avoid fully reinstalling windows as I have done a LOT of reinstalling over the past day, so any help would be greatly appreciated!!
Depending on you motherboard - you should be able to tap an F key during boot to choose the boot device—one of those boot devices should say windows boot manager-pick it and your Windows should boot normally.
This will give you the opportunity to back up important “cannot lose” data just in case.
Someone else here, with more knowledge than I on boot entry’s should be able to help out more but this should do it also: https://dev.to/je12emy/setting-up-dual-boot-with-windows-and-arch-linux-using-systemd-boot-2c24
I would wait until an expert chimes in before attempting anything in that URL.
I can advise you how to fix the Windows boot but then you’d lose the Linux boot.
What I posted above about BIOS boot entries should soothe your panic and show that Windows is still there and untouched.
Best to wait for an expert to chip in before going further than that using the URL I posted.
IF you decide to go further (I wouldn’t) using the URL → start at step one as systemd should already be installed (unless you changed that to grub during the install of EndeavourOS?)
There is a procedure you can run from a Windows Install ISO if you need to reinstall the bootloader, I’ll leave that to your searching ingenuity, because I certainly don’t remember it, though I do remember it consists of about 3-5 commands.
Very similar to bootctl type commands in Linux.
As an aside, it doesn’t seem that Windows is all that happy about partition modifications…i’ve noticed that myself 
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The Windows CD/Install ISO way to fix the boot manager will leave you without a linux boot entry—>that’s what I was going to advise you to do until i realized that Windows will take over the boot and Linux will need to be started using the F boot menu key of your main board.
I also found this on this forum: it is from 2023: again wait for an expert to chip in before trying something that may end up with data loss:
BUT-you do you.
Only YOU know how technically knowledgeable you are.
IF you feel you got his then please, don’t listen to me.
Cheers.
First, make sure you’re booting in UEFI mode if it’s a UEFI installation (if Windows has an EFI System Partition then it’s UEFI). In this case, if CSM or Legacy boot mode is on in your BIOS settings, try turning that off. Conversely, if it’s a BIOS mode installation (no EFI partition, and probably-but-not-definitely an msdos partition table), make sure CSM/Legacy boot mode is on.
If that’s not the problem, then you can download a Windows ISO file from Microsoft, and use a tool like woeusb or ventoy to burn it to a USB stick.
(To minimize the risk of Windows messing up your Linux bootloader in turn, I think people have had success with setting “hidden” and “no_automount” flags on the Linux EFI partition (if UEFI). But please look this up before taking my word for it because I’m just working off vague memory of things I’ve seen other people say here.
But at least, go ahead and make a backup copy of your Linux boot files to somewhere in /home, just in case.)
Boot from the USB stick, and click the option in the lower left that says “repair your windows” or something of that nature.
After that, the first thing I’d recommend trying is the Restore option. Hopefully, Windows Restore has automatically made a backup of your system (after a windows update or another installation) and you can just restore from that. You’ll lose any programs you’ve installed since the last restore point, but your files/documents should be okay.
If you don’t have a restore point, there’s an automated repair troubleshooter that may or may not work.
Last resort, you can pick the command line option and might be able to fix it with “sfc /scannow” and DISM.exe. I can’t remember precise DISM.exe directions unfortunately, but iirc you point it at a reference windows image, like the one in your usb, and at your broken install, and run /CheckHealth and /RestoreHealth. Use “dir” and “Diskpart” to figure out what disk/volume is where.
I think I’ve also heard of people doing something to add a Windows entry to a grub Linux bootloader, to boot Windows from the Linux bootloader instead, for what it’s worth. I don’t know anything about this though, so I don’t know if it’s a potential solution, but could be something to look into at least.
Are you saying that GRUB or systemd-boot or any other boot loader that you use, lists A Windows boot manager item but when you select it, Windows does not boot.
OR
GRUB or systemd-boot or any other boot loader does not list the Windows boot manager at all ?
Did you try to do what @MyNameIsNobody suggested to do? Namely
Did this work? The F Key will be either the function key F2 or F6 or F8 or F10 or F12. Try out all of these and let us know the output.