I'm having issues with the computer store I ended up going to for a custom built PC for my boyfriend. We ordered a nice PC for the price which included a copy of Windows 10 Pro. We had them put his old hard drive in the PC because he didn't want to lose all his games he's downloaded or any pictures, videos, or other files he has saved on it. Problem is when they put the PC together they forgot to install Windows on the new hard drive so his PC is running the copy of Windows from his old hard drive. That's not a problem to us. When they called to inform us of this mix up he didn't want to take his PC in again and lose time being on it so I asked if they could give me the product key to install the Windows 10 Pro on my PC since mine has a cracked copy & keeps telling me I need to activate Windows. They ended up saying yes & emailed me an invoice with the product key on it. I went to activate the key & it wouldn't take it. I called Microsoft and the rep on the phone said that it was actually a Windows 8.1 Pro key not a Windows 10 Pro key. He checked 3 times and came up with the same result all 3 times. I called the store and they said that it is a 10 Pro key but an OEM fresh install key which some times shows up wrong in Microsoft's system when you try to upgrade to 10 Pro. He told me that he could offer to have me bring in a flash drive to put Windows 10 Pro on it for me to boot from & install it on my PC. I did that. I got the same error that I got when I tried to just input the product key. It said it was not a valid license of Win 10 Pro. I called the store back. He offered to have me bring my PC in and just do an install of Windows 10 Pro on my PC at no cost. I got the PC back and noticed that it asked if I wanted to boot from volume 1 or volume 6 when I booted up. I didn't know what the difference was so I just said volume 1. Volume 1 was a fresh version of Windows 10 Pro but it had my OLD product key attached to it. I noticed that in addition to the C drive having Windows on it my SSD E drive now had my old Windows 10 Pro cracked version on it when it previously didn't have anything on it but 2 games. I called the store to let them know about this and they said that since THEY didn't build my PC they couldn't offer support to me about it. They said that the product key is tied to the motherboard and since I have a previous copy of Windows 10 Pro on my PC that their product key won't work on MY PC.
So this brings me here for advice. First of all, is that correct that using their product key it wouldn't work on my PC since I have a previous copy of Windows on my PC or are they just full of shit? Secondly if it will work on my PC, how do I go about reformatting my C & E drives to remove copies of Windows on it while still being able to put Windows 10 Pro back on my PC? I still have the flash drive with the bootable install of Windows 10 Pro to use or I could burn a copy of it on a DVD if necessary.
Thanks in advance for any help you can provide.