I think the 4.8.4 kernel does have some serious problems, I don't have the
model handy but on the kid's old Acer laptop it fails while trying to load
the initrd after about 10-15 seconds and reboots.
Even more strangely, even if I force power it off by holding the power
button for 4 seconds it still reboots about 10 seconds later... I've never
seen anything like it! Booting the 2nd kernel, left over from f23 (just
upgraded) works fine.
Thanks,
Richard