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Get the fix for "<strong>Operating System not found</strong>" boot error for <strong>Windows XP, Vista, 7, 8, 8.1 </strong>or<strong> Windows 10</strong>.

This error is also very common for Sony VIO laptops, including T-Series ultra books and S-Series.
<h2>About "<strong>Operating System not found</strong>"</h2>
[kbintro]
<h3><span id="Description_and_Symptoms">Description and Symptoms</span></h3>
The error messages, alerts, warnings, and symptoms below are tied to this error.
<h3>Symptom 1: "Operating System not found" error screen on startup</h3>
When a PC is booting, the BIOS tries to find a operating system on a hard drive to boot from. However, if it is unable to find one, then an "Operating system not found" error is displayed. It may be caused by an error in BIOS configuration, a faulty hard drive, or a damaged Master Boot Record.

<a href="https://neosmart.net/wiki/wp-content/uploads/sites/5/2013/08/operating-system-not-found-missing.png"><img class="alignnone wp-image-459 size-full" src="https://neosmart.net/wiki/wp-content/uploads/sites/5/2013/08/operating-system-not-found-missing.png" alt="Operating system not found error screen" width="980" height="536" /></a>
<pre>Operating system not found</pre>
Another possible error message is "<strong>Missing operating system</strong>". This error is also very common on Sony Vaio Laptops.
<h2>Causes of this Error</h2>
This error has been known to occur as a result of one of the following causes:
<h4><span id="Cause_1NTLDR_is_compressed">Cause 1: Bad BIOS configuration</span></h4>
Since this error occurs when BIOS is unable to find the operating system, checking the BIOS settings first is often a good solution. The BIOS configuration can become incorrect because of power outages, hardware errors or errors made when configuring the BIOS manually.
<h4><span id="Cause_1NTLDR_is_compressed">Cause 2: BCD is damaged</span></h4>
Similar to the errors outlined in the <a href="http://neosmart.net/wiki/bootmgr-is-missing/">BCD is missing</a> and <a href="http://neosmart.net/wiki/bootmgr-is-corrupt/">BCD is corrupt</a> articles, this error can also appear when BCD becomes damaged.
<h4><span id="Cause_1NTLDR_is_compressed">Cause 3: Faulty data cables</span></h4>
If the BIOS is unable to detect the hard drive, the faulty data cables are often to blame. Try to unplug, and then plug them back, or even replace them altogether and see whether the problem persists.
<h2><span id="Fixing_8220NTLDR_is_missing8221_on_Windows">Fixing "Operating system not found" on Windows</span></h2>
[setupcd]
<h3>Fix #1: Rebuild BCD via Easy Recovery Essentials</h3>
<div class="content dynamic_content_max_width"><span class="message_body">Easy Recovery Essentials’ one-click automated system repair corrects issues caused by corrupt BCD by recreating it from scratch on the active bootable partition. This is done automatically as part of the automated repair process, and requires no manual action or user intervention.
</span></div>
<div class="content dynamic_content_max_width">[easyre error="Operating System not found" bootscreen="xp-vista-7-8-10"]</div>
<h3>Fix #2: Change or reset the BIOS configuration</h3>
Since this error often occurs when BIOS is unable to find the hard drive, checking BIOS settings might be a good solution.

To check the BIOS settings, follow these steps:
<ol>
 	<li>Restart the computer</li>
 	<li>Press the necessary key to open BIOS menu. This key depends on the computer manufacturer and computer model. This is usually listed on the first screen that appears on the monitor. It can be any of the following: <kbd>Esc</kbd>, <kbd>Del</kbd>, <kbd>F2</kbd>, <kbd>F8</kbd>, <kbd>F10</kbd> or <kbd>F12</kbd>.</li>
 	<li>If the screen shows multiple keys, find the key to open “BIOS”, “setup” or “BIOS menu”</li>
 	<li>Check the BIOS' main screen to see whether it detects the hard drive, and the boot order to see if it is set correctly.</li>
</ol>
Here are the screenshot examples of BIOS' main screen, with a hard drive and a CD-ROM that were properly detected, and a boot order screen that has a hard drive in the first position.

[caption id="attachment_4379" align="alignnone" width="640"]<a href="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/BIOS-main-screen.png"><img class="wp-image-4379 size-full" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/BIOS-main-screen.png" alt="BIOS main settings screen" width="640" height="480" /></a> BIOS main settings screen[/caption]

[caption id="attachment_4380" align="alignnone" width="640"]<a href="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/BIOS-boot-order-screen.png"><img class="size-full wp-image-4380" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/BIOS-boot-order-screen.png" alt="BIOS boot order screen" width="640" height="480" /></a> BIOS boot order screen[/caption]

If the hard drive is not detected properly, consider replacing the data cables, or resetting the BIOS settings to default values. Here are the steps to reset BIOS settings:
<ol>
 	<li>Enter the BIOS screen by following the steps outlined above</li>
 	<li>Find the "Reset to default" or "Setup default" option - it could be either a hotkey, or an option in the menu</li>
 	<li>Choose the reset option, and answer "Yes" when prompted for a confirmation</li>
 	<li>Then, select the "Exit -&gt; Exit saving changes" option.</li>
</ol>
[caption id="attachment_4382" align="alignnone" width="640"]<a href="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/BIOS-reset-defaults.png"><img class="wp-image-4382 size-full" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/BIOS-reset-defaults.png" alt="BIOS reset defaults screen" width="640" height="480" /></a> BIOS reset defaults screen[/caption]
<h3>Fix #3: Run Automatic Repair</h3>
<span style="line-height: 1.5">The Windows Automatic Repair may recover certain boot process related errors in some cases. Here are the steps to access the Automatic Repair from an install disc:</span>
<ol>
 	<li>Boot from Windows install disc</li>
 	<li>Click <strong>Next</strong> in the setup page after selecting proper language, time and keyboard input</li>
 	<li>Click <strong>Repair your computer</strong> and select <strong>Troubleshoot</strong></li>
 	<li>Click on <strong>Advanced options</strong></li>
 	<li>Select <strong>Automatic Repair</strong> and select your operating system.</li>
</ol>
Here is an example of what the PC’s startup repair should look like once the BOOTMGR file is properly restored:
<div id="attachment_4353" class="wp-caption alignnone">

<a class="cboxElement" href="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/Compressed-bootmgr-fixed.png"><img class="wp-image-4353 size-full colorbox-4360" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2013/08/Compressed-bootmgr-fixed.png" alt="Compressed bootmgr fixed" width="800" height="600" /></a>
<p class="wp-caption-text">Corrupt bootmgr fixed by Startup Repair</p>

</div>
<h3>Fix #4: Rebuild the BCD using bootrec.exe</h3>
Just as with the <a href="https://neosmart.net/wiki/bootmgr-is-missing/">BOOTMGR is Missing</a> error, rebuilding your computer's BCD can fix boot loading issues.

Here are the steps to rebuild the BCD:
<ol>
 	<li>Boot from the Windows install disc</li>
 	<li>Click on <strong>Repair your computer</strong> after selecting proper language, time and keyboard input.</li>
 	<li>Select the Windows installation drive, which is usually <code>C:\</code>, and click <strong>Next</strong></li>
 	<li>Choose Command Prompt when the System Recovery Options box appears</li>
 	<li>Write the following command and press <kbd>Enter</kbd> afterwards:
<pre>bootrec /rebuildbcd</pre>
</li>
 	<li>If the program finds a Windows installation and asks whether it should add it to the boot list, press <kbd>Y</kbd></li>
</ol>
Here is an example screenshot of what the PC's console output should look like once Bootrec is done rebuilding the BCD.

[caption id="attachment_3693" align="alignnone" width="800"]<a href="https://neosmart.net/blog/wp-content/uploads/sites/5/2016/04/VirtualBox_Win7_clean_21_04_2016_03_58_48.png"><img class="wp-image-3693 size-full" src="https://neosmart.net/blog/wp-content/uploads/sites/5/2016/04/bootrec.png" alt="Bootrec utility results screen" width="800" height="600" /></a> Bootrec utility results screen[/caption]
<h3>Fix #5: Reset BIOS settings on Sony VAIO Laptop</h3>
The eSupport section of Sony.com suggests the following solutions if your VAIO laptop is showing this error:
<ol>
 	<li>Remove all removable media, e.g. USB flash drives, CDs, DVDs etc.</li>
 	<li>Reset BIOS settings back to default</li>
</ol>
Here are the steps to reset VAIO's BIOS settings <strong>if you have Windows XP, Vista, 8 or 8.1:</strong>
<ol>
 	<li>Remove any peripheral devices you may have connected to the laptop</li>
 	<li>Restart the computer and press the <kbd>F2</kbd> key when the VAIO logo appears</li>
 	<li>When the BIOS setup screen appears, press the right arrow key (<kbd>-&gt;</kbd>) to select the <strong>Exit</strong> menu section</li>
 	<li>Select <strong>Get Default Values</strong> by pressing the down arrow key</li>
 	<li>Press <kbd>Enter</kbd> at "Load Optimized Defaults"</li>
 	<li>In the <em>Load Optimized Defaults</em> make use of the arrow key to select <strong>Yes</strong> and then press <kbd>Enter</kbd></li>
 	<li>Again use the arrow keys to select Exit (Save Configuration) and press <kbd>Enter</kbd></li>
</ol>
Here are the steps to reset VAIO's BIOS settings <strong>if you have Windows 7:</strong>
<ol>
 	<li>Press and hold the <kbd>Assist</kbd> button after you restarted the laptop until the VAIO black screen appears on the monitor</li>
 	<li>When the VAIO Care Rescue Mode screen appears use the arrow keys to select Start BIOS setup [F2] and press <kbd>Enter</kbd></li>
 	<li>Press the <kbd>F9</kbd> key to reset the VAIO's BIOS to the original default values</li>
</ol>
<p class="info">In BIOS, make use of the arrow keys to navigate through the screens and options, <kbd>Enter</kbd> key to select an option and the <kbd>ESC</kbd> key to exit the active window.</p>

<h2>More Information</h2>
<h3>Linked Entries</h3>
<ul>
 	<li><a href="https://neosmart.net/wiki/bootcfg/">Bootcfg</a></li>
 	<li><a href="https://neosmart.net/wiki/bootrec/">Bootrec</a></li>
 	<li><a href="https://neosmart.net/wiki/vaio-recovery-disk/">VAIO Recovery Disk</a></li>
 	<li><a href="http://neosmart.net/wiki/bootmgr-is-missing/">Bootmgr is missing</a></li>
 	<li><a href="http://neosmart.net/wiki/bootmgr-is-corrupt/">Bootmgr is corrupt</a></li>
</ul>
[partial name="partial_moreinfo" versions="xp,vista,7,8, 10"]