boot device not found

Do you have a disk in the drive that the computer is trying to boot or USB sticks attached to the system? Remove them all.

Any difference?

At first glance, either the drive has failed or the partition on the drive has been damaged/deleted.

Do you have a Windows installation disk?

If so, you should insert it and try to repair your system if the Windows installation starts.

I don't think Windows will be able to repair itself but you can try.

If the repair process completes but is unsuccessful then at the screen that appears after Computer repair, you should try to select the dos prompt.

In the DOS window, type Diskpart (then press enter)

Now type List disk (and press enter)

Is your boot drive detected. detected?

Type Select disk 0 (and press enter)

Is drive 0 selected? If not then I'm afraid it's the drive.

otherwise:

Type List partition (then press enter)

Are there any partitions listed? If there aren't then a deleted/damaged. partition is the problem

How many?

But at least your drive isn't toast.

You may have to reinstall Windows, though.