no sound.

I keep having this problem of disappearing sound. There are no speakers, so I have to use headphones, but I need them for other things, so I can't keep them connected all the time. Resolve often loses the connection when they are unplugged and putting back doesn't bring back the sound always.

sometimes I restart the program, or the computer indicates that something has been plugged in and I select headphones and OK, but still no sound. Only in resolve, I can hear training videos fine. Audio is not muted, where do I go to get the audio back.

Hook up a set of speakers with a headphone jack.

Hook up a set of speakers with a headphone jack.

Or buy a second set of headphones

Maybe someone knowledgeable will know why only Davinci Resolve does this, instead of those just trying to rack up post numbers.

Rob, how have you got your audio set up? I'm not sure if this is a Realtek thing or a Resolve thing. With speakers plugged in the Realtek Volume Mixer shows Resolve as a separate input using the built in Realtek audio, all be it with a pair of Dell computer speakers attached, but I can also plug and unplug headphones without any problem. So it seems Resolve requires that dedicated connection to be there.
I would suggest that you get yourself some computer speakers, preferably ones with a volume control and headphone socket on them. This would give you the best of both worlds. Failing that consider an external interface such as a Focusrite or Behringer as they not only give you audio I/O but a dedicated headphone output as well.
Is your audio configuration set up properly? Picture shows how I have mine set up in Resolve.

I got the Resolve sound back by changing the selected input from headphones to headset it seems. On my older PC, with firewire, I actually have a semipro recording situation with cubase and 3 Firestudi Projects, each with 8 inputs. I have lots of speakers and a couple of combinations hooked up to this system. None of them have plug ins, all bare wires. there is not even room on the desk for more speakers currently. I haven't gotten to the point yet of opening up the new Dell to see if the Firewire can be put in it and use that for my main audio too. So meanwhile, while trying to catch up on 6 months of unprocessed video, I'm just getting started thus. A lot of the sound is horrendous wind noise that I've tried to reduce with EQ.

As you've a lot of video to process that has wind noise you should consider a third party option such as this.
https://acondigital.com/products/restoration-suite/#:~:text=DeNoise%202%20is%20a%20plug,in%20the%20noise%20profile%20mode.

Thanks Charles, that picture was useful as I saw that my headphones were not selected and changing it thus enabled sound without having to restart Resolve.

Previous suggestions to leave the headphones plugged in, buy a new pair, so I don't have to change for my other computer, would have been a waste of money, as I found that when Resolve went to sleep after finishing a video export, the sound was gone again though the headphones weren't unplugged. I suppose the next suggestion would have been to never let it sleep or turn off.

Well, some programs like Resolve do not respond well to hibernation or sleep modes as when waking up not all processes will restart automatically. It's best not to let your computer go to sleep when Resolve is open.
My Windows Power Plan is set to High Performance with the monitors and computer set to Never Sleep. All my USB ports' power management settings are set to not turn off either.

I downloaded the suggested noise reduction software and sent them an email asking why after installing it doesn't appear in my apps to try.
On my last clip I had used Blackmagics Noise reduction and it had improved things. On a new timeline I tried to repeat, selecting all the clips but it seemed like it created a new noise reduction box for each as I kept closing and there would still be a window till finally they were all gone. I don't know what was different this time. I want it pretty much the same across the timeline.

Selecting a group of would mean you get a separate Noise Reduction window for each so that they can be adjusted individually.
For audio you can do it on a track basis.

Noise Reduction-Audio.jpg (73.96 KiB) Viewed 1103 times

Noise Reduction-Audio2.jpg (260.08 KiB) Viewed 1103 times

You would do the same with a third party VST app.
For video you can do it with an Adjustment Clip.

Noise Reduction-Video.jpg (348.57 KiB) Viewed 1103 times

If you downloaded and installed a VST app it should appear here in Preferences/Audio Plugins.

It's best not to let your computer go to sleep when Resolve is open.

very true. in fact, there are a number of apps that don't always wake up correctly after sleep - me included;-)