Referring to Windows 7 install from ISO image.

Computers with preinstalled versions of Windows 7 have the OEM version. Are you sure an OEM product key will work with these — presumably retail — versions of Windows 7?

Yes, MS doesn’t separate OEM from Retail discs anymore starting with Vista. Any valid key will work to activate, there is even a way to do a fresh install on a new drive with an upgrade key using a few registry hacks.

Few registry hack? Or more like 1 registry editing, changing a value from 1 to 0, to say that a previous version of Windows was detected.

1- HKEY_LOCAL_MACHINE/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/, and edit MediaBootInstall from 1 to 0.

2- Run command prompt as true admin, and execute: slmgr /rearm

3- Restart your computer, enter product key in the activation box, and activate Windows.

This is only required if you wish to do a clean install on a computer with an upgrade product key.

During setup windows checks for the presence of a “Windows” folder on ANY of the fixed disks (even if you wish to reformat the drive using the setup tool). If it finds one it will set that bit to 1. That will allow it to accept an upgrade product key.