Yes, it's true that reinstalling (repair, repair, clean install) usually helps, but it doesn't always have to be the first thing to do.
Among other things, it would be very important to know how Windows is installed (normal, VM, double boot, etc.) and also whether you are using legacy boot or UEFI boot.
It is also worth noting that there are often situations where Reset computer or onplace reinstall (preserve files and apps) also does not work, because the shadow copy is also damaged or missed at all, or registry is damaged. Then is good to have registry backup, what people usually don't have.
In this case, you need to boot from an external device (USB, DVD, etc.) and back up your files and more. Otherwise you will lose everything.
Have You looked is the boot order and boot configuration OK?
And one more thing, have you tried boot in safe mode or repair booting files?