You needed the retail key that ashish.k provided to activate under digital entitlement. Your install was probably using an oem key by default...
It will (should) work. I have tried it because what you are trying to do here I have done it (Change from MBR to GPT). The key I gave is a generic retail key for Win10 Pro. Everybody with digital entitlement gets it. It will only activate "upgraded" PCs. Another thing is you saying every time "I tried it again a couple times, however the offer to upgrade to Windows 10 doesn't appear." You don't have to do it that way. Just get an ISO of Win10 Pro x64, extract it on your HDD somewhere and run the setup.exe manually to upgrade. If you need clean install then make bootable USB and install. Try activating a couple of times until it doesn't. Sometimes it takes a few tries to activate as MS servers are lazy in this regard.
If you read thread, he's on Win 10, already activated, just wants to Format to GPT and clean install, he already has HWID
Next time please use the"Reply with quote" button. It will quote the person you are replying to, thanks
I know that but did you read the last part on his post? He wants to switch to GPT and clean install now. This reply is for that.
HWID is good forever on same computer, unless you change motherboard, fresh install and GPT don't matter, activation is stored on MS Servers.
Yes, but if your performing a CLEAN install with oem media then you would get the default oem key - not the Retail key.
Well everything worked out fine. I fresh installed and formatted to GPT. It activated as soon as LAN drivers were reinstalled. Thank you all for your help and suggestions!