Boot Device Not Found; Please install an operating system on your hard disk

[Matuush_]

Hi,

I have a big big problem.

As you see from my subject, it tells me to install an operating system on your hard disk. I searched some information on Google and also on YouTube, did many tutorials and all was the same. After Enabling the Legacy support, I putted in that 4 number code + enter and nothing happened. I have black screen with “_” on len side showing me once per second,

any help please ? 

Thanks.

[WAWood]

@Matuush_ 

If your PC came with Win10 preloaded, then it was configured in UEFI mode -- and changing it to Legacy mode will ensure that it will NOT boot anymore.  You have to change it back.

This issue is often due to a failing drive. So, let's check that first, because if it is failing, it would need to be replaced and there is no point then in doing anything else until we confirm that.

If your PC is new enough to support UEFI, you can use these steps to test the hard drive: http://support.hp.com/us-en/document/c00439024

If not, to check the drive you have to follow these steps:
1) Press Esc key repeatedly, several times a second, while rebooting the laptop. Do NOT hold the key down, just press it over and over.
2) Eventually, you will see an HP Startup Menu
3) Press the Function key for testing the hard drive (usually F2) and let it run.