Are you getting a 0xc1900201 error installing Windows 10? I got both that and 0xc1900200. Here’s how I fixed it.
I upgraded my venerable Dell E1505 to Windows 10 over the weekend. It was harder than it needed to be, but I got it running. It’s an old machine, but the CPU is fast enough to run Windows 10, and if you max out its memory and put an SSD in it, I think it may even run Windows 10 better than it ran Windows 7.
Here’s how I got it working. The same trick may work if you have a different older machine as well.