Missing Operating System Not Found
In most cases, this happens when you install Windows Vista or later operating systems in conjunction with older operating systems. For example, Windows XP used Boot.ini and Vista onwards it was BCD Edit.exe located in the Windows\System32 folder. There can be two scenarios here. You will need to boot with the disk, and repair Windows.
Here is what you can try. Boot the Windows Installation Media, choose Repair and then Open a Command Prompt window. In Windows 10 you can also access the Command Prompt via Advanced Startup Options. Now enter the following commands one after the other and hit Enter after each: Reboot your Windows system. This should hopefully and have made your problem go away!
For more details see KB927392 and read this post on Bootmgr is Missing in Windows. If you receive Error 1962 No operating system found message, you may have to replace a possibly faulty HDD or your SATA cable. This post will help you if you receive an Application not found message. See this post if you see Invalid System Disk, Replace the disk and then press any key message. Related reads:
