I don't have a product key.

[99saugat]

😥Oh! Thanks. The shop owner gave me the laptop with prewindows 8. I installed windows 10 after formating hard disk. That means, no luck. 

[99saugat]

Oh! Thanks. The shop gave me the device with pre installed windows 8. I installed windows 10 after formating my hard disk. That means, no luck.☹️

[Paul_Tikkanen]

You're very welcome.

Yes I'm afraid so, because there is no product key in the BIOS.

If there had been a Windows product key in the BIOS you could have installed W8/8.1 and then upgraded to W10 for free.

It is too bad you did not have a record of the installed key before you formatted the hard drive.

[ieee488]

If the dealer had installed Windows 8.1 and Windows 8.1 was activated when he sold the laptop to you, then,  Windows 8.1 should activate again if you re-install Windows 8.1 of the same type since Microsoft servers have a record that your laptop had a license for Windows 8.1.

.

[99saugat]

Oh! Thanks.

[Paul_Tikkanen]

Hi, @99saugat 

You will need to have an actual W8.1 product key to activate W8.1.

Microsoft will have no record of your PC being activated unless you re-enter the key that was used to activate Windows.

Now, if the PC shop still has that product key (they should have given it to you in the first place), then you can see if they will give you the key, or a key you can use to activate Windows.

There are two instances where you don't need a product key to activate Windows.

1. If the product key is in the BIOS (W8 - W10).  Your notebook's BIOS does not have a Windows product key.

2.  If you previously upgraded from W7, W8, W8.1 to W10.

Then you can use the method I had posted previously.

You can temporarily reinstall W8.1 with a generic key that will be good for 30 days.

If you don't have W8.1 installation media, download the plain W8.1 ISO file from the link below.

https://www.microsoft.com/en-us/software-download/windows8ISO

Use the Microsoft tool that I zipped up and attached below that you will need to transfer the ISO file to a DVD or USB flash drive so that it is bootable.

Enter this generic key for the standard version of W8.1:

334NH-RXG76-64THK-C7CKG-D3VPT

After W8.1 has completed installing, you can install the drivers and available software from your notebook's support page.

https://support.hp.com/emea_middle_east-en/drivers/selfservice/HP-15-Notebook-PC-series/7486447/mode...

Then you will have 30 days to figure out how to get the official W8.1 product key you should have gotten.

[99saugat]

Anyway, I have to get the product key.

[Paul_Tikkanen]

Bottom line...that is correct.