If you don't have your product key have a read through here and see if you can extract it from your windows 7 drive.
How to Find Your Lost Windows or Office Product Keys
Then came the MS free upgrade to Win10. Knowing I hated Vista and so Windows 8.1 (Another story for another time!) I decided to use the blank former Vista drive for Win 10 and keep Win 7 as long as I could, while learning to love Win 10!
I guess when I used the reformatted previous Vista drive, it was treated as a fresh install. Why then can I not boot my Win 7 HDD (with the Win 10 HDD disabled)? It begs for an explanation, as they are not RAID cohorts? I wanted to preserve the dual boot Win 7 and Win 10. I think Win 10 is set up to seek and destroy it's ancestors! A Tojan horse of another kind.
But dual boot is definitely possible by initially carrying out the simple install of Win7, 8 or 8.1 on to drive 0 (as described by Sherlock) and making sure it is activated correctly. Then you can move forward with making a dual-boot system.
As long as Drive 1 retains a full version of Windows 7 stored on it, you can restore booting from it. You can try installing Macrium Reflect Free. It has an option under tools to find non-booting OS and fix booting to them. That's about the easiest way I've found.
But be careful, messing with booting like that will change what gets upgraded or installed over. That's why I think try to install Win 7, 8 or 8.1 over existing Win 10 now is the easiest and safest.
Sorry I have limited OS skills and it is holding me back from moving forward. I do not know how long I can go on with a non activated Win 10, which allows me to do 90% of the day to day needs. As "Why Me" said right off the bat, it is my top priority to get it activated.
My needs are to get win 7 pro and Media Center working to get OTA TV. going again. If I understood the Macrium Reflect repair routine, it may better than risking the Win 10 that works for now and having my PC dead!
I will look into Macrium Reflect Free.
Now to figure how to install Win 7 Pro over Win 10 Pro and get it activated for free! I want the Win 7 Pro for it's Win Media Center to get my OTA Tv going!
I will always install OS with just one drive working. The other will have it's cables pulled. Once bitten twice shy! Whatever the outcome I need one Win 7 with Media Center and One with Win 10 Pro dual boot.
Install Macrium Reflect Free in Windows 10. Under the tools Menu option, you will find the utility to fix boot problems,. It should find your Windows 7 and then highlight it and add it to your boot menu.
Then boot into Windows 7 and run showkey from this forum to retrieve your Windows 7 product key.
Then we'll go from there.
Thanks NavyLCDR .
I will venture to do as you suggest. I may need some respite, as our kids and grandkids have invited us to join them at a cottage next Friday. I have to get my 2002 Buick Regal checked out for this 600 km round trip into the north.
I got a terrible scare this morning. My Windows 10 after booting came up with Critical error notification. The error was that neither my Start nor Cortana are functioning. I could open some files, but not programmes No Task or start up at the bottom either. After several attempts to restart as suggested, I used CCleaner to check for registry errors and it rebooted OK. The Cortana thing is weird, as it is not yet released for use in Canada.