Windows not original, but it is

Hello, I have the following problem.

I have a laptop with Windows 10, original, as it came with the computer. I was checking out an activator for Microsoft Office and now Windows says that the System is not activated and has that annoying message on the bottom right corner of the screen.

How do I activate it back to how it was before? Again, I had a legitimate copy that came with the laptop but now it says it is not original.