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[VAIO_PC] It shows “Operating System Not Found” and cannot startup Windows

What do you do when your VAIOPC displays “Operating System Not Found” and you can not start Windows?
After you turn on the power, “Operating System Not Found” is displayed and you can not start Windows.
After changing the BIOS settings, “Operating System Not Found” is displayed and you can not start Windows.
After initializing the BIOS settings, “Operating System Not Found” is displayed and you can not start Windows.

We will check the connection status and the BIOS settings of the peripheral devices

Applicable Products
VAIO PC General

Description
If the “Operating System Not Found” error is displayed and you cannot start Windows, it may be due to a problem with the BIOS settings of your peripheral devices which are interfering with the computer’s ability to read your hard drive. Please attempt the following procedures to resolve.

Method of operation
1. Make sure you do not have an external drive or a USB device such as a USB flash memory connected.  
If you do have any of these devices connected to your PC, please remove the external device and restart the computer.

If the external drive or USB device is mounted, the computer may try to load the operating system from the external devices and an error will be displayed.  You must remove the device and restart the computer.  If the hard drive is set to the highest priority when loading an operating system, it is possible to boot the computer even when you have a USB device connected.

2. Make sure the HDD or SSD has been recognized by the OS
1. If that does not fix your problem, press the power button while holding down the F3 or F4 key.
2. . The “VAIO rescue mode” screen should appear so you can select the BIOS settings.
If a password has been set, please enter the password.
3. Make sure that the main menu is displayed in the BIOS setup screen.
4. Check to verify that the hard drive is being recognized
If the hard drive is being recognized properly you will see your hard drive’s size in GB (for instance it may read 256GB or 500GB). If “None” or “0GB” is displayed, then your hard drive is not being recognized by the computer. If this is the case, please contact your Service Center.
If the computer is able to recognize your hard drive, press the left and right arrow keys and choose the “boot” menu.

3. Check to verify your boot configuration
If you are using Windows 8.1, your startup configuration should be listed as UEFI.
If you are using Windows 7, your startup configuration should be listed as Legacy.
Ensure that your settings are appropriate for the OS you are using.  If the wrong settings are selected you will not be able to start windows and the “Operating System Not Found” error will appear.

1. You can use your arrow keys to navigate your BIOS menu.
*depending on your model, you may be able to use your mouse.
2. After selecting the appropriate settings for your OS, you should have two options “Exit and Discard changes” or “Save Configuration Changes and Exit”. Save your changes and exit.
3. After changing the settings, restart your PC to check to see if you can boot to your operating system.
4. If your hard drive disk is able to be recognized and you have changed the above settings and you still cannot boot to your hard drive, please attempt to recover your system.
▼ related Q & A
 [Windows 10] How to perform recovery (re-setup/initialization)