After trying all sorts of things suggested in Microsoft and HP troubleshooting steps, I came across an HP forum in which a problem of no sound after upgrading to Windows 8 or 10 from Windows 7 was presented. The cure was as follows and it worked for me tonight:
"If your notebook has 4 GB of memory, I know you are not going to believe this, but for some crazy reason having 4 GB of memory installed on that platform causes the sound not to work.
Try this workaround for that if your notebook has 4 GB of memory...
A problem with the Conexant audio means that you may hear no sound in Windows 10 even though everything appears to be working correctly.
Microsoft suggests running msconfig.exe and heading to the Boot tab. Click the Advanced options button, check the Maximum memory box and set the value to 3072."
If you don't know how to get to msconfig.exe, there are a variety of instructions on the internet. I just typed it into the Win10 search box. Not sure if Cortana lets you do that since I disabled mine. Make sure you reboot. You should hear the Windows theme play when you logon with your password. Tada!
I hope it works for you too.
Linda