Software & Apps Windows How to Fix the 'Operating System Not Found' Error Don't worry, your files are probably okay! By Tim Fisher General Manager, VP, Lifewire.com Tim Fisher has 30+ years' professional technology support experience. He writes troubleshooting content and is the General Manager of Lifewire. our editorial process Facebook Twitter LinkedIn Tim Fisher Updated February 01, 2020 Windows The Ultimate Laptop Buying Guide Tweet Share Email If your computer can’t find an operating system to boot into, you might see a very simple error against a black screen that reads “Operating System not found”. This might be a startling error to see. How were you able to use your computer just fine before the error, but now the operating system is just gone? Where did it go? Are your files gone, too? Fortunately, there are some really simple reasons this could happen, and it’s very unlikely that your important data has been erased. Here are some causes for the “Operating System not found” error: BIOS has been misconfiguredBoot records are damagedThe hard drive is damaged or unreachable The “Operating System not found” error can be seen on any computer running Windows 10, Windows 8, Windows 7, Windows Vista, or Windows XP. How to Fix the “Operating System Not Found” Error Restart your computer. The “Operating System not found” error could be a temporary glitch that a restart will fix. Disconnect unnecessary flash drives, eject the disc if there's one in the disc drive, and remove any floppy disks. Your computer might be trying to find a suitable OS on one of those devices, and if it can't, it might display the “Operating System not found” error. Boot into BIOS and make sure the hard drive the operating system is installed on is listed as the first boot device. If it's not, change the boot order so that it is. This is important because if something else like a flash drive or disc has priority but doesn’t have an operating system on it, your computer will assume that there isn’t an OS to boot to and it will throw the “Operating System not found” error. Toggle UEFI Secure Boot on or off, depending on what it's set at right now. Whether Windows can boot in UEFI mode depends on whether it's on a GUID Partition Table disk or an MBR disk. Enabling or disabling Secure Boot can determine if the error is related. You do this through the BIOS setup utility (see the link in Step 3 to learn how to get there) through the Security tab. Toggle Secure Boot to whatever it currently isn't, so either Enabled or Disabled. Restart your computer after this step. If you're still seeing the “Operating System not found” error, revert this setting back to what it was and continue with the next suggestion below. Reset BIOS back to factory default settings. Undoing every BIOS customization might reset something that was previously hiding the hard drive or corrupting how the operating system could be found. The easiest way to fix the “Operating System not found” error with a BIOS reset is to look for a reset option within the BIOS setup utility. It might be a function key like F9 that you need to press, or a menu option called Reset BIOS. The specific steps you need to take depend on the BIOS manufacturer. Repair the boot records to fix the “Operating System not found” error. Valid boot records are vital for a normal boot process. If the master boot record (MBR) or boot configuration data (BCD) store are corrupted or missing, you might see the “Operating System not found” error. Since you can't access Windows due to the error, you'll need to use an installation disc or flash drive to get to the repair tools that we talk about in this step and the next one. Learn how to do that in Windows 10 and 8 here; Windows 7 (here) and Vista users (here) can follow similar steps. Start by rebuilding the BCD with this command (open that link for all the steps you need to get to the Command Prompt where you can type this): bootrec.exe /rebuildbcd While you're still in Command Prompt, after the previous command finishes, enter this one: bootrec.exe /fixmbr Finally, reboot your computer to see if the “Operating System not found” error has been fixed. See how to repair the MBR in Windows XP if you're using that version of Windows. Another way to fix some Windows XP boot files is by repairing the boot.ini file. Use the diskpart command to activate the partition that Windows is installed on. For whatever reason, it could have become disabled, which would explain why you're seeing the “Operating System not found” error. Access Command Prompt from the installation CD by following the same steps as above, and then enter this command: diskpart Followed by: list disk Use this command to pick the disk that corresponds to the one the operating system is installed on (most people will see just one in the list): select disk 0 Use this command to list all the partitions on that disk: list volume Enter this one to pick the partition on that disk that Windows is installed on: select volume 2 Make the volume active with this command: active If you've fixed the “Operating System not found” error, Windows should start normally when you reboot. Exit Command Prompt and choose Continue to try starting the operating system. Reseat the hard drive's power and data cables. Unplugged or loose cables could be the cause of the “Operating System not found” error. Reinstall the Windows operating system. The “Operating System not found” error might be literal. It's possible that malware or an unintentional format has wiped the OS from the hard drive. If you can't access the hard drive to reinstall the operating system, Step 10 is your last option. At this point, a faulty hard drive is the only remaining reason for why you're still getting the error. Replace the hard drive and install a fresh version of the operating system to fix the “Operating System not found” error.