Hello all !

I'm currently helping a friend upgrade an old prebuilt PC (new GPU, new PSU, more RAM) that runs Win7 by default, and I'm stuck at the free upgrade to Win10 step (using the Assistive technology loophole).

Win7 was (cleanly) installed on the SSD (64GB) before attempting the update. Windows occupied roughly 30GB of the drive.
Once the upgrade process is initiated, the tool downloaded Win10 in the background and then proceeded to actually doing the upgrade just fine. I'm watching the progression % by %. A few reboots along the way, all is well.
Around 45% though, the screen suddenly went black. No spinning circle, no mouse cursor nothing. The monitor still picks a signal, but it's just emply blackness.
I've waited and waited (nearly 2 hours now) and still nothing.
It's to be noted that I've already attempted that free upgrade that twice, with the same results.

I eventually got an idea : what if the SSD is actually too small, and that in the process of writing Win10 files, the SSD just ran out of place, crashing the installation process ?
First question : Do you think this might be the issue ?
EDIT : Apparently not, I tried the upgrade on another, bigger drive and it failed exactly at the same moment.

That PC is a prebuilt, comes with an OEM Win7 licence (sticker on the side). We've already re-activated it via MS automatic online tool when cleanly installing Win7 before all that.
Second question : Do you think I could use that automatic tool once again (if attempting to install Windows on another driver for example) or would they block it because twice in the same day ?
EDIT : apparently yes

Thanks in advance for any answer !

EDIT : Follow up question : Can an OEM Win7 key be used to activate a fresh intallation of Win10 ?
I'd say no, but hey, you can always hope.

EDIT : YES GODAMNIT !