This error often occurs due to boot order issues or a damaged boot sector. Check BIOS boot settings, reconnect the hard drive, or use Windows recovery tools to repair startup files.
To fix the "Operating System Not Found" error in Windows, check BIOS boot order, ensure the hard drive is detected, repair the Master Boot Record using Windows Recovery, or reinstall Windows if necessary to restore the OS properly.
Fix Operating System Not Found by confirming the BIOS boot order, re-connecting the drive, using Startup Repair, repairing boot records with bootrec commands, scanning disk errors or reinstalling windows where necessary.