This answer is for those with UEFI who have deleted the Ubuntu partitions before removing grub

You will be doing this from Windows 10. No bootable media required.

Where bootrec /fixmbr, bootsect /nt60 and the Ubuntu live with the boot-repair suggestions have failed, this has worked for me:

(This answer borrowed verbatim from here)

1. Run a cmd.exe process with administrator privileges
2. Run diskpart
3. Type: list disk then sel disk X where X is the drive your boot files reside on
4. Type list vol to see all partitions (volumes) on the disk (the EFI volume will be formatted in FAT, others will be NTFS)
5. Select the EFI volume by typing: sel vol Y where Y is the SYSTEM volume (this is almost always the EFI partition)
6. For convenience, assign a drive letter by typing: assign letter=Z: where Z is a free (unused) drive letter
7. Type exit to leave disk part
8. While still in the cmd prompt, type: Z: and hit enter, where Z was the drive letter you just created.
9. Type dir to list directories on this mounted EFI partition
10. If you are in the right place, you should see a directory called EFI
11. Type cd EFI and then dir to list the child directories inside EFI
12. Type rmdir /S ubuntu to delete the ubuntu boot directory

Assuming you only ever had two operating systems (Win 10 & Ubuntu) you should now be able to boot directly to Windows without hitting the black grub screen.

To restore Win 10 default bootloader follow these steps:

• Log into Win 10
• Open Command Prompt (Admin)
• c:\> bootsect /nt60 <drive name>: /mbr

<drive name> is the drive letter where the Master Boot Record (MBR) will be updated

For example to update C master boot record this is the command:

c:\> bootsect /nt60 c: /mbr

For more help about bootsect command see here -

You can restore the Windows bootloader with a Windows 8/8.1 DVD. These instructions are inspired by Manindra Mehra's answer, but I expanded it with full working details (verified with a Windows 8.1 DVD).

1. Put the DVD in your optical drive and boot from it.

2. Press a key when it displays Press any key to start from CD or DVD.

3. Select your language etc. and click Next.

4. Click Repair your computer.

5. Click Troubleshoot.

6. Click Advanced Options.

7. Click Command Prompt.

8. In the command prompt window, type bootrec /fixmbr

9. Click the red X to close the command prompt.

10. Click Turn off your PC.

11. Turn the PC back on and it should boot directly into Windows.

This leaves the Ubuntu partition on your hard drive or SSD. To remove it:

1. Hit Windows+X and select Disk Management.

2. Find the Ubuntu partition. It will probably be a large partition without a drive letter.

3. Be sure you have the correct partition!

4. Right-click the partition and delete or reformat it with a Windows filesystem.

Remove Boot Loader EFI / System Partion in Windows 10

Quick Guide

Open PowerShell as Administrator

mountvol S: /S
S:
cd .\EFI\
dir
rd /S Ubuntu