Does the sticker affixed to your system say Windows 8 or Windows 8 Pro? Does the Edition say Windows 8.1 or Windows 8.1 Pro? It sounds like Dell send out the wrong Edition of installation media. Lets try to resolve this first I advise first making sure your BIOS is up to date revision A13: [URL] See here to determine your (UEFI) BIOS revision and update. Ensure UEFI and SecureBoot are enabled: [URL]#BIOSRevision Next you have a choice install Windows 10 TH2 or clean installing Windows 8.1. Installation Media from Microsoft will not ask for a product key and automatically pick up your UEFI BIOS embedded SLP key during installation provided the Edition of the Installation Media and your Product Key match. Simply put if you asked for a product key you are installing the wrong Edition. I advise Windows 10 TH2 over Windows 8.1 see here for details on your Free Upgrade from Windows 8.1: [URL] To Download Windows 10 TH2 installation media see here: [URL] To Download Windows 8.1 installation media see here: [URL]  
I have an XPS 8500 that came from the factory with Windows 8.  Soon after the purchase (around first of 2013) I made the rescue disks on 4 DVDs.  Recently the hard drive failed.  I gave the Dell salesman the service tag #  and ordered a new hard drive.  I Asked what I needed to re-install the OS.  I was told I needed a USB key ($39.99) and ordered one.  I was told this would get me up and running.  I installed the new drive and inserted the USB key.  Windows installed and runs.  However, I cannot activate Windows.  Using Belarc advisor I was able to find my Windows key imbedded on the bios.  When I input that key the pop up tells me that the current edition is Windows 8 Pro and the current product key ends with QPBRC.  This differs from the product key embedded in the bios and I get an error code of 0xc004c003 'the activation server determined the specified product key has been blocked" and that I need to purchase a new key.  I'm assuming that the problem is that I have a valid key for Windows 8 but not Windows 8 Pro. I called Dell and was given a number to call Microsoft; alternatively, I was told that I'd need to go through Dell's tech support at a cost of around $250.  I am at a loss at this point.  Any suggestions are welcome! 
Windows activation problem