To date, I have attempted to upgrade six Win 7 machines to Win 10, four laptops and two desktops, with two successes and two failures, both via the online upgrade and using the previously downloaded bootable DVD or USB installation drive. Before starting, I downloaded all the latest drivers for all machines.
On two HP laptops, one 64 and one 32 bit, the upgrade was smooth and flawless.
On two others, it went through the entire upgrade process, on rebooting, each machine gave the same unidentifiable error message and restored the system to Win 7.
The same errors happened on both desktop machines, one Intel and one AMD based, both with an online upgrade and when using my bootable DVD.
With nothing to lose, I next tried a clean installation, using my Win 7 key, on a formatted drive on one of the desktops, and the results told me a lot. I had no problems with the base installation. The installation completed and booted to the Win 10 desktop, but I got an error message that my nVidia video driver was not compatible with Win 10. I downloaded the latest Win 10n compatible driver (on another machine), and that solved the problem.
Then, I had problems connecting to the web. Finding and installing the latest Realtek Win 10 network driver for my chipset resolved that issue, as well.
On the second desktop, I just cut to the chase and went for the clean installation which required exactly the same updates for both video and network drivers.
When I had earlier tried to upgrade the first laptop, (before I did the clean installations, I tried to beat the system and install the Win 10 drivers while still running Win 7, and I ran into a "gotcha' moment. The network driver installed well, but the new video driver was not compatible with Win 7, and I had to reboot to safe mode to uninstall the driver and re-install the previous version just to attempt.
I don't know about AMD video drivers, but one problem I've encounterd with trying to do this with laptops is that some nVidia video drivers are tweeked for specific laptop graphic systems, and they will not allow updating from from any source other than the laptop manufacturer. If this happens, and you can't find Win 10 drivers, stay with Win 7.
My conclusion is that a clean installation is the best way to go, but do it on another drive so that if everything falls apart, you can just stick your old drive back in the machine and get back to work or play... whichever comes first. If you need more partitions on the drive, do that first, and install Win 10 on your preferred partition.
Hope that helps.
