When you computer is booting, the BIOS will find a system on your hard drive to boot to. If there is not any system, the computer doesn’t know where to go, so it gives you a message for troubleshooting. Below are the main reasons why Windows operating system is missing.
1. The computer input/output system (BIOS) does not detect the hard disk drive.
2. The hard disk is damaged or corrupted.
3. Master Boot Record (MBR) on hard drive is broken. Note that some third-party programs or disk operations can damage an MBR.
4. An incompatible partition is marked as Active.
5. A partition that contains the MBR is no longer active.