On a Toshiba Satellite Laptop, which had converted from Windows 8.1 to Windows 10 without difficulty, I allowed the conversion to 10 Anniversary Update.
On one occasion the computer restarted after getting a "bugcheck", and then looped in the restart. I got it to come up normally by holding down the power button for at least five seconds.
Toshiba Service Station has pestered me to uninstall and reinstall a new version of some specialized firmware, which I do not understand .
One problem is that Microsoft (unlike Apple) has to work with to many vendors. When rolling out massive operating system changes, problems with firmware are inevitable. Many home users don't have the coding or technical skills to maintain all this on their own, the way corporate IT departments would have.
In its effort to add unusual interactivity for users (and embellish the chat assistant Cortana, who is rather like an AI science fiction character) Microsoft is creating a world that many ordinary users don't have the necessary technical skill (aka Edward Snowden) to maintain.