What not to do in Windows 10!

OK, let this be a lesson to us all! Recently at work I was required to remove Windows 7 and roll a Notebook back to Windows 10. It came with restore media which did not work - why? Because we originally had the notebook on the Network where we are 'guests' (not to be confused with guest account), the IT guys flatten the hard drive completely before installing a Windows 7 Enterprise image - so no 'factory restore' partition present. So having phoned the 'Dell' Support helpline only to be told, "Your laptop is out of warranty" (at which point I corrected them, Notebook - as their US site correctly states!). Whilst trying to resolve the situation, I somehow managed to get my call switched to Airplane mode (don't know how that happened!) So I get an email about useful help page on restoration. Lo and behold! A chance to download an image of Windows 10 to a memory stick - I downloaded the installer app and had to take this home to do, together with works memory stick for the purpose of downloading the image to. Now I had forgotten that works memory sticks currently available were only 4 Gb in size - so I had to use my 64 Gb Patriot Drive - as I had some 25 Gb of useful items I did not want to lose, and the Windows 10 drive being flakey, I decided to boot into Windows 10 hard drive, then backup to my Windows 7 Pro drive in User | desktop. "You don't currently have permission to access this folder. Do you want to make it permanent?" "Yes" - BIIIIIGGGGG MISTEAK! (pun/typo error intended!).
After backing up my memory stick, I then proceeded to download the Dell image. Job done I decided to boot into my Windows 7 Pro drive. Windows logo appears, then ....
Black Screen and a mouse pointer - Nada! Fortunately, no forced shutdowns so my trusty Zorin Lite 12.4 could access my User folders so backed up everything important to external drive. So now I have FerenOS on where Windows 7 Pro used to be... but inside FerenOS I have Virtual Box which has, Windows 7 Pro so that evil Windows 10 will not be able to force an upgrade oh yes, on the C:\drive was a folder that had not previously existed, 'Win10upg' - now I wonder what that stood for!