Windows 7 Product Key after Reformating

So I am planning to reformat my hard drive because its performance has been reduced to trash lately. My biggest concern is that I purchased Windows 7 upgrade as a student offer from Digital River and I still have the product key but Digital River seems to have discontinued having the file on their servers.

Anyways I managed to find the now provided ISOs but now I am worried about my product key. From what I understand, the offer was an upgrade so there are a few questions raise:

• Can I use the product key to validate a clean install?
• Do I have to install Vista first, via recovery, then install Windows 7?
• Most importantly, can I use the product key more than once? Provided I format the hard drive of the original machine.

Google has lead me to mixed results of yes-no's and I would appreciate clarity.

I think this should answer your question Clean Install with a Upgrade Windows 7 Version

No you don't have to reinstall Vista as when you boot the Win7 installer to reinstall, it will see an OS which is all that's needed to allow use of Upgrade version key during install. Otherwise to install to a wiped or blank HD you'd have to do the workaround given in the tutorial linked in post above.

You bought a retail copy which you own for the life of the OS to reinstall as often and wherever you want.

You can adapt these steps to Clean Reinstall Windows 7 Factory OEM to get a perfect clean reinstall of your retail version, too.