New
#21
If you have a readable Product Key on the purchased PC's COA sticker then that can be used to Clean Reinstall Windows 7 as it details in the blue link tutorial, and which has been used by over 1.2 million consumers without a single complaint or failure to activate.
You do not need to use the Upgrade version Product Key provided by your friend if there is already a license with the PC's you bought. There seems to be something wrong with the Upgrade Product Key anyway, or else it should work.
But is the friend's Upgrade copy for the same version that is on the COA sticker Product Keys that came with the PC's? If not, then extract the ISO, unlock all versions, and burn to DVD or write to flash stick as detailed in Step 1 of Clean Reinstall Windows 7 . Then select the licensed version during install, make sure you input the Product Key correctly, and it will always activate.
Finally, I don't know why MS is telling you they don't sell Win7 any longer since you already own two licenses and were given a third. You are entitled to reinstall those copies of Win7 for as long as the keys are readable and I have never seen it fail if the correct version and Product Key are used.