In Settings in Windows, goto "System -> Sound -> Volume Mixer" and click the "Reset sound devices and volumes for all apps to the recommended defaults" reset button. Try it with Opera open and with Opera closed.
I have un-installed Opera and and installed a new one
Do you also choose to delete your data when uninstalling when you were asked? If not and the problem is with your data/settings, an uninstall and reinstall alone won't help. In both "C:\Users\yourusername\AppData\Roaming\Opera Software" and "C:\Users\yourusername\AppData\Local\Opera Software", you can rename the "Opera Stable" folder to "Opera Stable old" to start with fresh data and settings.
You can goto the URL opera://settings/reset and reset just your settings. You might lose your open tabs despite Opera saying otherwide, but it might help.
Even if your settings look fine, there might be something in the "Preferences" file that's messed up where resetting settings might fix it.
You can goto the URL opera://flags and reset your flags.
You can disable the "Hardware media key handling" flag at the URL opera://flags/#hardware-media-key-handling to see if it helps.
You can see if a test standalone installation has the issue too or not.