When restarting my MythTV box after being shutdown, the machine died, releasing the Magic Smoke, after investigating I found that the PSU had failed.
I'll have to give a history of what's happened after this:

While testing, I removed the Capture cards to eliminate where the problem was, so after restarting the box with a new PSU, it fired up OK. So replacing the cards and restarting, lead to the root window login for mythtv-setup. I had to recreate the cards, but I noticed that I had to reset the location of where the recorded files would be (/myth/tv) from what appeared to be a path to an NFS share. I assume this was due to the fact the system automatically reconfigured itself to being a frontend rather than a combined Frontend/Backend box.
So exiting and logging in I had to reset the theme and OSD back to standard 5D1 defaults. In MythVideo and MythMusic Setup I had to reset the directories to the normal directories (/myth/music and /myth/video respectively).

So when trying to use BurnDVD (CD/DVD --> Burn DVD), it came up with the following error message
I found the following http://mysettopbox.tv/phpBB2/viewtopic.php?t=10772&start=0&postdays=0&postorder=asc&highlight=cannot+mythburn+work+directory as a solution.

I found that recordings did not seem to save the position when playing back, I had to reset the Action On Playback Exit in General Playback (Part2) Settings to "Save Position on Exit".
When trying to playback a DVD, it just went to a black screen, then returned to the frontend. So looking at the Media Settings for DVD, I found that player had been reset to mplayer, so I changed the player back to xine with the following:

Something interesting seems to have happened with the machine name, I had changed it using the instructions elsewhere on this site, previous to this, somethings seemed to have reset themselves to the previous name, so I had to reset the entry in MythWeather for my location.
Because of this, it seems I've ended up with 3 phantom encoders, as follows (from MythWeb):
Though, everything seems to working OK.

Hope this is able to help someone in a similar situation.

Bruce S.

_________________
Updated 2019/10/26: AthlonII X2 265 Gigabyte GA-970A-DS3P
16Gb PC 1866 DDR3, 500GB+2TB+4TB SATA HDD,
SATA DVD-RW Asus DRW-24D5MT , NVIDIA GeForce GT1080
Hauppauage Nova-T 500, Nova-T LinHes R8.6.1

Before changing the PSU, or maybe during the troubleshooting stages? Everything you described sounds like the hostname was changed on the system (the output of 'uname -n'). The hostname is used extensively throughout the mythconverg database, as that is what is used to identify different systems.

If the current hostname for your system didn't exist in the settings table when you got the system back up and running then everything would appear as default.

It was a while before the the initial shutdown mentioned, everything worked well after the name change.
That makes sense, it looks like the machine name change never "took" for some reason to stay set after a shutdown.

Bruce S.

_________________
Updated 2019/10/26: AthlonII X2 265 Gigabyte GA-970A-DS3P
16Gb PC 1866 DDR3, 500GB+2TB+4TB SATA HDD,
SATA DVD-RW Asus DRW-24D5MT , NVIDIA GeForce GT1080
Hauppauage Nova-T 500, Nova-T LinHes R8.6.1