If your computer refuses to boot or displays errors like "Operating System not found," a damaged Master Boot Record (MBR) is often the culprit. You can fix this using built-in Windows tools or dedicated third-party software.
This is the most direct method and doesn't require downloading extra software if you have a Windows installation or recovery USB. Hard Drive Mbr Repair Software
bootrec /fixmbr — Writes a new Windows-compatible MBR to the system partition. If your computer refuses to boot or displays
bootrec /fixboot — Writes a new boot sector to the partition. Hard Drive Mbr Repair Software