It sounds like you don't have one. Or it would be mentioned rather than what you are getting.
How To Fix "Operating System Not Found" or "Missing Operating System" error.
1. You will need your Windows OS (Operating System) CD or bootable Windows OS USB device.
2. Connect the bootable USB device or insert the CD into your computer.
3. Now use the "F2, F12 and Delete" keys enter BIOS setup.
4. Click "Repair Your Computer" below the "Install Now" button.
5. While you are in the "Repair Your Computer" open "CMD" (Command Prompt).
6. When you are in "CMD" type “diskpart” then type “list volume”.
7. Next you will be in "list volume". All volumes should be shown.
8. Find your system volume, where the windows are installed and then type “select volume ###“(system volume C) shows on CMD. Ex. select volume 3.
9. After you have selected the volume, type “ACTIVE“. Your system partition is active now.
10. Now type ”exit” to leave diskpart and then type ”exit” again to close CMD.
11. That’s it now RESTART your computer.
This should work, if you follow the steps correctly.
NOTE: When typing in anything, do not include the quote "" marks, otherwise things will not work correctly.