I understand that you are looking windows 7 product key to reinstall window
Here’s what you need to know:
OEM Copy: If your computer came with Windows, it likely has an OEM copy. An OEM copy is tied to a specific computer and can’t be moved to a new computer. While you’re free to upgrade a PC’s hardware components or replace a failing hard drive, you can’t move your OEM copy to a new computer.
Retail Copy: If you purchased a boxed copy of Windows, it’s likely a retail copy. A retail copy of Windows can be moved to a new computer, but you’re only allowed to use that copy of Windows on a single computer at a time. That means you’d have to uninstall the old copy of Windows before you moved it to a new computer.
Don't worry, though, as I'll be glad to help you out as you could attempt activating your windows using the following methods:
Activate by phone (IVR) using Microsoft:
Step 1 – Click on Windows Orb and enter ‘slui.exe 4’ into the search box
Step 2 – From the search list, click on ‘slui.exe 4’
Step 3 – From the drop-down list, choose the country you are residing now
Call the designated toll-free number; Read out the number displayed on the screen accordingly.
The IVR will then read out a list of character to you, enter it into the screen and Activate windows.
Reinstall windows using the recovery media that you may have created shortly after the computer was purchased, if you haven't that's okay as you can order one online using the Official HP Website: Click here