Windows 10 install fails alongside Windows 7

Question

I recently got ahold of a T450s which came stock with Windows 7, and I'd like to leverage the Windows 10 upgrade. I know that Windows 10 still has some bugs to be worked out, however, so for safety's sake I'd like to have 7 around as a backup.

To begin, I downloaded the upgrade tool onto Win7 and upgraded that to 10. So far so good. I then use that 10 install to make a bootable 10 USB drive.

I should say here, that if I delete all the existing partitions, I can (and have) used this media to clean install and activate Win10 by itself. Doing such a clean install works perfectly.

That done, first I start clean, restoring Windows 7 from lenovo USB media. This creates three partitions: sda1 is "SYSTEM_DRV", presumably with the boot stuff, sda2 is "Windows7_OS" and sda3 is "System Recovery".

Next, I shrink sda2 to make room for Windows 10. (I've also deleted sda3 at this stage). I boot off the Windows 10 install media, select the empty space or create a new partition in it (tried both) and the whole first phase completes, copies things to disk, and then it gracefully restarts itself. I think it's supposed to have altered or replaced the boot menu so I can get back to the partition to resume the process, but this doesn't happen and the machine boots back to Win7. I've tried to manually boot to the new partition with a grub disk, but it generally throws an error.

I've installed multiple Windows installs of prior versions with this method before and never had an issue. What could be going wrong?

Answer 1

You didn't state that you'd activated the initial Windows 10 installation. MS has changed the licensing process, requiring activation through registration of hardware, before a clean reinstall is possible.See How to Clean Install Windows 10.