Do a clean install and add no extra apps. Then when it is working well, add one at a time until you have the problem. I know, I know some folks use literally dozens of apps, but the rule is the more apps the more problems. Any idea why the sound is not working? Often it is a jack broken off in the sound out connection for externals, or maybe incorrest system preferences set up. Have you ever ran Recovery Mode over the Mac? Start up in Command and R, go to Utilities and run Disk First Aid and see what is reported.. Next option is to tke it to a Genius Bar or Apple Store for a free diagnosis. often if Safe Mode works it can be restored.
For old Mac users, remember how we used to disable extensions loading, and adding a few at a time until the problem reared its ugly head and was isolated?