On Tue, 18 Dec 2018 11:20:15 -0500, Charlie
wrote:

On 12/18/2018 12:48 AM, Char Jackson wrote:
On Mon, 17 Dec 2018 23:03:53 -0500, Charlie
wrote:

Have you tried raising the CPU voltage slightly? My ASRock Z270 Extreme
will reboot on startup if the CPU voltage is too low.
It's worth a try although I'm at a loss to understand how it would boot
from a DVD.

Well that was an interesting suggestion. The default setting for vcore
is Auto, which resulted in a vcore voltage of 0.971v. Google seems to
indicate that 1.35v is probably the upper ceiling for the Core i7-8700,
but values of 1.1v to 1.3v are usually selected in order to keep the
heat under control.

Taking somewhat of a chance, I set vcore to Fixed (versus Auto), then
entered a value of 1.1v.

The system booted without issues from the Linux DVD, but it has done
that before. I shut it down and reconnected the SATA HDD, leaving the
optical drive connected, and tried to boot from the HDD. It booted
perfectly! That's the first time it has been able to boot from the HDD.
Now I'm letting it run through some boring routine admin tasks, such as
creating system snapshots, making and suggesting a list of software
packages that could be updated, etc. It's been running from the HDD for
about 3 minutes now, and that's a huge leap forward. [Edit: It's been
running for over 30 minutes and still going. Amazing!]

I'm glad it helped.

What are you running for vcore? Also, Fixed or Ratio or ?

Vcore on mine is set to Auto which sets it at 1.216v. I have an I7
7700K 4.20GHz 4 cores.
I only got the reboot problem when I 'played' with the voltage, lowering
it to see how low it would go before it stopped working. If I recall
correctly it got down to just under 1 volt when it started rebooting.

In a previous post, I remember saying that I trust the defaults. Grrr...

I still don't understand why it worked when booting from a DVD.

Paul offered the theory that when I was attempting to boot from the HDD,
the power draw was higher than when I was booting from the DVD. Only
marginal, perhaps, but enough to tip things over.

I'll do additional research today to see what's considered optimal for
the i7-8700 (non-K version), then manually set it. It's currently 1.1v,
but I won't be surprised if the consensus says to use something closer
to what you're using, say 1.20 to 1.25v.