The Win 10 upgrade went ok on my Acer Aspire 7538 notebook (Intel Core 2 Duo, 2.2 GHz), after I spent hours trying to upgrade, only to have the Win 10 download, fail, part way through.
Finally found out that it was a WIFI problem???? Once I used a network cable, the Win 10 download worked fine.
Then I tried to boot into the notebook BIOS, but no way!!! Just kept booting into WIN 10. WT.......
The bios on this notebook is an older, standard bios, not a UEFI bios.
After many hours of Googling for an answer, I finally found out that the problem was the Win 10 hybrid boot!!!!
The hybrid boot was too fast for the computer BIOS to start up, with the F2 key press.
I found some instruction on how to go into Win 10 and disable hybrid boot.
Now I am able to get into the BIOS, to set the Boot parameters, etc. :-)