After a virus attack, you need to reinstall the OS, but there is no Windows license activation data.

[Andrii_Boyko]

After a virus attack, you need to reinstall the OS, but there is no Windows license activation data.

[TheOldMan]

If you PC came with Windows 10 or it has had Windows 10 installed and was activated, then you do not need Windows license activation data, as it will auto-activate when the Windows is reinstalled.  If it had Windows 10 installed when it came from HP, then you might be able to use the HP Cloud Recovery -

https://apps.microsoft.com/store/detail/hp-cloud-recovery-tool/9MTKS9PR7R3N?hl=en-us&gl=us&rtc=1

However, you can also make the Windows 10 install

If you need the install media for Windows 10, you can make it from this Microsoft download

https://www.microsoft.com/en-us/software-download/windows10

With a working PC, scroll down to the "Using the tool to create installation media"
and then follow the directions. You can make either the DVD or USB. Use this new media to install Windows 10.
When the install asks for the product key, click the "I don't have a product key" option to continue,
then the install will continue. It will be activated once it connects to the internet, as it uses a digital key.