Can't find Activation Key for Windows 7 ISO from Digital River

I first purchased Windows 7 Home Edition (32-bit), then upgraded online to Windows 7 Pro (32-bit).
The hal.dll corrupted and I couldn't fix the problem because I only had the Home Edition discs.

Several sources in Forums advised me to fix the problem using a boot disk from an ISO downloaded from Digital River.
That disc couldn't fix the hal.dll problem either so I did the Custom Install. That put a new installation of Windows 7 Pro on the computer.
Now I'm being asked for the Activation Key. The Key I was given when I upgraded to Pro isn't being accepted. I'm told that the Key I was given only works for the Windows 7 Pro upgrade..!

I've signed-on to the Microsoft site and followed links around for a while, but I can't find any understandable information about my problem. How do I get the Activation Key for Windows 7 Pro now that it's been reinstalled?

Thanks

Can you point me to more information about that? My paid product failed and I was forced to replace it and now I can't find a way to get an Activation Key for this OS obtained legally from Digital River. All I did was replace a broken Windows 7 Pro with a working copy. Is there a specific reason why I can't provide proof of purchase to Microsoft and get this current installation Activated?

I don't think I need to do Option Three in that example. I'm not getting an Error Code 0xc004f061. I'm not getting any error codes at all. I'm just told I need to Activate the OS.
I think I should change the Product Key. I've looked through the files on the boot disc I made from that .ISO, but I don't know what I'm looking for. I'm just guessing, of course, but if I could figure how to get a Product Key for the OS that's installed now, maybe I can get an Activation Key for that.
Do you know where I could find that Product Key?
Thanks

The Activation prompt isn't accepting the original Product Key. It says that the Windows 7 Pro product key I'm giving it pertains to that upgrade, not to the software that's installed now.
So I've paid for Windows 7 Pro, which failed, and was replaced with a copy from Digital River, which I can't Activate maybe because I need a different Product Key. I didn't see any mention of any of this when I downloaded that ISO and reinstalled from the boot disc. And like I said, I'm just guessing that maybe this is the reason for the trouble.

Thanks

Yes, that's correct.
It started with a "hal.dll" error message. The OS wouldn't boot. I put out 'feelers' on a few Forums and the most common replies agreed that I should download Windows 7 Pro .ISO from Digital River and from that boot disc attempt to fix the hal.dll problem.
I went down the list of options on the menu supplied by the boot disc but nothing worked to fix the problem, and the final option was Custom Install. So that's what I finally did since nothing else worked.
Over the last several days I've been reinstalling all my applications, getting everything setup again...

Thanks.