Solution: Operating System not Found when Turn on PC/Laptop

When the computer starts up, a black screen appears with the message in the upper left corner of "Operating System not found". This error occurs because the BIOS does not find the Operating System installed on the hard drive, even though you are sure that the Operating System has been installed on the hard drive. So why does this error occur.

There are many possibilities for an Operating System not Found error when turning on your PC / Laptop

1.  BIOS settings changed

        BIOS settings change due to two factors:

        -  The BIOS settings have changed because the CMOS battery has run out.

        -  BIOS settings changed by the user.

2.  Hard disk not detected

Solution

1.  BIOS settings changed

To enter BIOS setup, press F2/Esc/Delete after pressing the Power button. After entering the BIOS, see the date settings. If the written date setting is wrong (different from the current date), the conclusion is "BIOS settings returned to default". Look at the picture below.

If now is November 2020, while the System Date is written: [01/10/2013] the conclusion is that the BIOS returns to default settings. When the BIOS returns to default, not only the System Date changes, but other BIOS settings also change, one of which is Boot Mode. Look at the picture below.

For example: Default BIOS setting for Boot Mode is UEFI

There are two options in Boot Mode settings, namely UEFI and Legacy. If during the installation of the Windows Operating System for Boot Mode settings you use "Legacy", when the CMOS battery runs out, the Boot Mode setting will return to the default, namely "UEFI".

The conclusion is that the "Operating System not found" error occurs because the Boot Mode setting returns to the default, namely "UEFI" while the Operating System installed on the hard disk uses the "Legacy" BIOS setting. Changed BIOS settings are due to "dead CMOS battery" indicated by "wrong System Date BIOS".

The solution to this problem is to replace the CMOS battery with a new one, followed by resetting the BIOS to the correct settings (matching System Time, System Date, and Boot Mode), then Exit and Save the BIOS settings. Look at the picture below.

Note:

-  For Windows 7, Boot Mode = Legacy

-  For Windows 8.1, Boot Mode = UEFI or Legacy

-  For Windows 10, Boot Mode = UEFI or Legacy

Boot Mode settings for Windows 7, 8.1, 10, are adjusted to the initial settings when installing Windows Operating System into hadisk.

For example: The installed Operating System is Windows 7 with Boot Mode "Legacy". When the CMOS battery runs out, the BIOS settings return to default "UEFI". After replacing the CMOS battery with a new one, open Boot Mode settings, change from UEFI to Lagacy.

2.  Hard disk not detected

Another cause of an Operating System not found error is an undetected hard drive. When the PC/Laptop is turned on and the BIOS does not detect the hard drive, an "Operating System not found" error message will appear. The cause of the hard drive not being detected is a dirty hard drive connector, or the hard drive connector is not installed properly. To solve an undetected hard drive, follow the instructions in the image below.

On a Portable Computer

On a Laptop/Notebook

Operating System not found errors are caused by changing BIOS settings, or the hard drive is not detected. If the BIOS settings remain the same, it means that the other possibility is that the hard drive is not detected because the hard drive connector is dirty, or the hard drive connector is not installed properly.

Tutorial Video