Got it installed finally on the PC that was having this problem (an Acer Revo R3700 with Windows 7 x64 Home Premium). The overall upgrade experience was horrible, and the successful attempt took about 5 hours, and it needed intervention to hard reset the computer after it locked up with a black screen (in the installing drivers phase), but setup resumed after than and it got there in the end. Massive contrast with my main desktop (a much faster PC) which took about 1/2 an hour, once initial download problem solved.
What I did was:
Installed off a USB flash drive created with Rufus from the Windows 10 ISO.
Set Windows 7 to "clean boot" using msconfig
Ran a disk check and defragmented the HDD
Ran System File Checker - sfc /scannow (got the all clear in this case)
Uninstalled Nvidia display and chipset drivers - allowed it to install default (WDDM?) drivers
Downloaded and ran the relevant version of the System Update Readiness Tool
I allowed it to download updates as part of the install, and did not disconnect from the internet.