My laptop can't boot?

Hi! I removed the Ubuntu today, but I couldn't get the Gnu Grub. I saw a tutorial that didn't solve my problem, but I knew how to boot Windows. Well, but I still wanted to remove Gnu Grub and did everything exactly as this article says: https://smarttechnicalworld.com/remove-grub-bootloader-from-windows/

And now my computer is broken. It starts up again after showing the following message for a second.

What can I do? This is very important!

You will need to reinstall the operating system.

It's up to your operating system - you just have to reinstall it

Here a

But if you did it this way it should work:
https://smarttechnicalworld.com/remove-grub-bootloader-from-windows/

Try the Computerbild Emergency DVD. There would be all the tools on it that you need. (Is Linux based without having to install Linux)
Starts automatically when you set "First boot = DVD drive".