I can relate. Got an undefined error code. Well .... that's helpful.
I've tried the upgrade from the little window icon down on the right hand side and that's failed twice on two different machines. It's a complete waste of time to go through the whole download only to have it fail time and again.
I found something that does seem to work smoothly though ......
Make sure that you're running an ethernet cable directly to your modem.
Just use a standard wired keyboard & mouse.
Use a standard monitor.
Temporarily pull and video cards.
Disconnect any usb devices like external hard drives and so on.
Next, use the media creation tool to create a usb thumb drive. After it's done being made, plug it into your machine and proceed to windows 10 setup. Do a completely new install. Don't to try bringing your files & apps forward into win 10.
This seems to work if you dumb the machine down enough.
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