Windows 10: What do i do?

I was in the middle of playing Fortnite when the application kept toggling out of full screen randomly for around ten minutes. After I get up from when it happened again I go back to my monitor and it’s on the blue windows installation where you would boot it up… I’ve had this pc running fine and playing games since fall of 2022. I tried the steps you would do for reinstalling however it’s saying that it cannot be done and woild just take me back to the beginning of the windows install. I do not know what to do and cannot find any similar issues anywhere. Any solutions or advice I will be than

:)