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I have just installed Ubuntu 18 on my Asus ROG I also have windows 10 on my hdd (and also had id before ubuntu). After installing ubuntu I had some problems getting grub to actually show up and let me choose which OS it should boot into.

Now, when I try to boot into windows I get a black screen with a blinking cursor. but fortunately I can still boot into ubuntu.

I could also mount the windows partition and see that is intact, so the OS still is there.

My question is how can I repair the windows bootmanager (i think this is the problem here) from ubuntu. Thank you!

I have also downloaded a windows 10 iso image and wrote it on a usb stick, but when I try to boot from the stick, it just freezes and the asus logo remains stuck on the screen.

marked as duplicate by karel, Eric Carvalho, Fabby, Kulfy, Charles Green May 4 at 4:08

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    Are you sure you installed Ubuntu in the same UEFI mode as the original Windows? – GabrielaGarcia Apr 17 at 15:01
  • No, dumb me forgot to check it before installing.. – ivanciprian Apr 17 at 15:01
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  • Probably Ubuntu is in Legacy... But you should be able to boot Windows as well as long as you change the UEFI settings and select Windows for first boot. Installing Ubuntu in UEFI mode will allow chainloading the Windows bootloader correctly from Grub. – GabrielaGarcia Apr 17 at 15:04
  • Ome thing I forgot to mention is that Grub displays FreeDos (dev/sda) instead of Windows 10, which seems to be mounted on /dev/sda2 – ivanciprian Apr 17 at 15:08
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Later edit:

After trying a lot of different solutions, here's how I finally solved it, in case anyone else has the same problem. Follow along and you should be able to boot into Windows again without losing any of your data.

  1. I created a bootable Windows DVD (I've tried with a stick also, but for some reason it wouldn't boot; for you, a USB stick might work)
  2. When setup starts, click next and follow the instructions until you reach the point where it asks you where you want to install Windows.
  3. Format the partition on which Ubuntu is installed.
  4. Continue installing Windows to the formatted partition (the one in step 3)
  5. Wait for the setup to finish. When the setup is done it should boot into the newly installed Windows version
  6. Once you are logged in, go to Computer and make sure that the old Windows partition is there. If it is, everything's all right, you can continue. Make sure to remember the letter associated with it (for example D:)
  7. Install EasyBCD (you can find it here: https://www.techspot.com/downloads/3112-easybcd.html)
  8. Launch EasyBCD, press 'Add New Entry' and name it however you like. For 'Drive' choose the letter at step 6)
  9. Once it's done, go to 'View Settings' to make sure that the settings have been saved.
  10. Reboot. Now, you should see the newly created option. If everything is all right you should boot into the old Windows wihout any problems. The following steps are optional.
  11. IF you want to remove the newly installed Windows, install EasyBCD and remove the boot option from the boot menu (from 'Edit Boot Menu')
  12. Run 'diskmgmt.msc', format the partition you've just installed and extend the current partition. You're done

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