So I tried installing Win 10 on a normal HDD, things didn't go well. I had an old back-up on another HDD, but it didn't have all my stuff up to date. So I lost a few things, at least most of them, I can re-download. I'll just install Win 10 when I get a SSD.

Moral of story: Always back-up before install/updating an OS. Unless you're doing a fresh install on a blank HDD/SSD.