Upgrade From Dubious Windows 7 License to Legit Windows 10 Pro

My son recently brought over a dead PC ( fried PSU and fried additional HDD). I was able to get a good Corsair PSU on sale and removed the dead HDD, leaving the boot HDD in the pc. The computer booted into Windows 7 and so I decided to use the creation tool to upgrade it to Windows 10 pro and purchase a key. As Windows 7 was not legit, the tool refused to upgrade to Windows 10. I figured no biggy, I would just use the tool to blow away whatever was on the HDD as all the data was backed up.

I started the computer and selected the USB stick as boot device but instead the computer booted into Windows 7 and now I got the message that Windows 7 needed to be repaired. This was unsuccessful as the license wasn't legit and so I restarted the pc, again I selected the USB drive by pressing f8 and this time the selection screen for windows showed up with the options: "Start Windows 7 Normally" or "Attempt to Repair Windows 7". I really had no desire to attempt a repair which was pointless in any case so I googled for the issue, no joy.

I could have pulled the HDD and put in another but I was determined to use the existing drive. With a wonky Windows 7 install, troubleshooting the drive was not an option. So, what to do?

I installed Linux Mint on the drive, took all of ten minutes and blew away the troublesome Windows 7 install. Once that was done, the pc now booted into the media drive, and I was able to install Windows 10 pro, I purchased a license and all is good. While this was successful, was there anything that might have made this a bit easier? Other than a new drive? I just cannot figure out why the computer kept booting into the Windows drive instead of the USB stick. The computer is an older home made build, with an ASUS M5A78L-M/USB3 MB.

Normally, I would boot into the standard Windows 10 USB flash drive and just delete all the partitions on the disk on the screen after selecting the custom install option. It's hard to say why the computer would not boot from the Windows 10 USB flash drive.

I searched for secure boot in the bios but I couldn't find it. One thing I did notice, after installing Linux and trying again, it took quite a while for the USB stick to actually start booting. In any case, it's all fixed now, I just posted here, in case anyone else runs into the same issue, not likely as most people have already switched to 10 and are probably already looking forward to 11.