Recovering OEM license information from HP notebook serial number

As explained in our Windows 7 Activation FAQ, OEM licenses are usually preactivated using System Locked Preactivation (SLP). If you use any HP OEM Windows 7 installation disk, it should activate automatically for you. Because of how the SLP process works, you don't need to know your key, because the activation occurs automatically if your machine is verified to be an HP.

You can also purchase a Windows 7 Recovery Disk from HP if you don't have access to one yourself. This is based on your computer's serial number, not the product key, because their database knows what version of Windows came with your PC.

If you do not have the original disk (as you stated), or have otherwise recorded it, there is no way to get that key back. I know of no manufacturer, even if you had support, who records and maintains that.