Missing operating system

[Sonu17]

Missing operating system

[Lil_Boy_Blue]

Hi

Missing OS can be linked sometimes to a failed/failing Hard Drive.

Can you please tell us what you can about the make, model and OS.

Do you have any kind of backup and/or recovery media?

[WAWood]

@Sonu17

These problems are generally due to one of two basic problems:
1) Failed hard drive
2) Corrupted/missing boot loader files
 
As to the first, please follow the directions in this link for testing your hard drive http://support.hp.com/us-en/document/c00439024
 
If that confirms your drive has failed, then you need to replace it.  Please report back if that is the case.
 
As to the second, you will need access to a working PC for this step in order to create the media needed to repair your PC boot loader.
 
Once you have that, please download and create Win10 install media from this link: http://windows.microsoft.com/en-us/windows-10/media-creation-tool-install?ocid=ms_wol_win10
 
Note that when you go do download and build install media, the tool defaults to matching what is already installed on your PC (as in, Home for Home, 64-bit for 64-bit).  While you CAN change these settings, do NOT. If you do, the resulting media will be different and will force you to enter a NEW product code!
 
Boot from the media you created, and follow the directions in this link: http://www.tenforums.com/tutorials/2294-advanced-startup-options-boot-windows-10-a.html
 
You will need to go to the Advanced Options screen and click on Startup Repair.  You will probably have to run Startup Repair three times for it to fix all the boot loader problems.
 
When done, your PC should boot OK. If it does not, there is a more serious problem.

[Wolf665]

Turn off the PC with the power button. Then turn it on and immediately press the F11 key repeatedly. The Choose an option screen opens.

On the Choose an Option screen, click Troubleshoot.

Click Reset this PC.

If you want to keep your personal files and customizations, click Keep my files, then click Reset. Your computer reinstalls the operating system and your computer restarts. You are done.

Keep my files and Remove everything options
Selecting keep my files:

    Keeps your personal files intact when reinstalling Windows 10.
    Deletes all apps and drivers you installed.
    Removes all changes to settings.
    Deletes all HP apps that came preinstalled on your computer. HP apps are reinstalled if your PC came with Windows 10.

If you want to remove all files, click Remove everything and continue to the next step.