nvidia 304 and fc23: black screens after updating today

[stan]

No expert, and I don't run nvidia anymore, but I'll try to help.

On Tue, 11 Oct 2016 00:00:00 +0100
John Pilkington <J.Pilk at tesco.net> wrote:

> This is the same system that had nvidia problems during its fc22 >
> fc23 upgrade.  That was reported here and solved on 30 June.  Since
> then it has been working well, but after installing the new packages
> today I get black screens with kernels 4.7.3, 4.7.5 and 4.7.6

What new packages were installed?  

> 'dnf downgrade xorg-x11-drv-nvidia-304xx --allowerasing' apparently 
> completed but then akmods-shutdown errored.  After re-upgrading, 
> akmods-shutdown completed, and the nvidia flash screen flashes, but
> then all goes black again, for all installed kernels.  I'm using tty2.

I'm not clear on what you are saying here.  What does "nvidia flash
screen flashes" mean?  And how are you using tty2?  By default, Fedora
always uses tty1 during boot.  Are you in multiuser, and running startx
to get to graphical?

> Xorg.0.log looks ok apart from 'ACPI: failed to connect to the ACPI 
> event daemon' and suggests looking at the ConnectToAcpid and 
> AcpidSocketPath options, which I have not yet done.  I don't know if 
> this is likely to be the real problem.

Unlikely.  ACPI is the power management daemon.  It shouldn't prevent
the driver from working properly to access the monitors.  You could
disable any screen savers you have enabled to be sure; if they are
taking effect immediately it might cause blank screens, even though the
driver is working.