Some but not all system sounds gone awol!

I've been doing fine with Win8.1 x64, until a few days ago. At that time there were two changes, one of which I assume to be the culprit. (1) a succession of Windows updates, and (2) my installation of HitmanPro Alert (HMPA) in place of Malwarebytes Anti-Exploit.

Then it crept up on me that I wasn't getting the system beep when I clicked on a program window when I had a dialog box open from that program. The program window title bar would flash, but no sound. Then I realized that I was without the very useful Toggle Keys beeps. Subsequently I found that also the Critical Stop sound was missing in this situation. Not all system sounds were missing - for example, the device connected / disconnected sounds.

This is NOT a matter of sounds having been turned off, at least in the standard manner. When I open the Sounds applet I find all my system sounds are still correctly configured, and all that I test there do play. Also, opening the "Making the keyboard easier to use" section in the Accessibility Centre shows Toggle Keys still enabled - and turning that feature off, applying the change, and then turning it back on and applying the change doesn't make any difference.

It is thus clear that something is blocking those particular sounds or disabling them in a non-standard manner.

I tried uninstalling HitmanPro Alert, and sometimes then got the sounds back after a full shutdown of the computer (but not just a reboot), but currently have now had two computer sessions (full power off in between) without HitmanPro Alert installed, and the sounds have not come back. So, my jury is very much out as to whether HitmanPro Alert is the culprit, though I still have a gut feeling that it is in some way involved, through having changed something on my system that has caused the problem.

I've tried Internet searches for other reports of such an issue, but the search listings are full of stuff about how to turn the sounds on or off (i.e., in the standard way), with no reference to the sort of issue that I have here - so it's too much of a search for a needle in a haystack.

Has anyone else experience of this particular issue and finding a means for resolving it?

If updates are involved the quick fix is to run the restore point just before the updates. If that is not possible you can try uninstalling the updates one by one.

Windows Update - Uninstall an Update - Windows 7 Help Forums

Ah yes, thank you, I am aware of that. However, that would all be a time-consuming performance - and I'm mindful that it won't be at all long now before my Win8.1 gets upgraded to 10, so it's probably not worth all that hassle in the meantime. Actually, if more or less nobody else has been experiencing the same issue since the recent spate of Win8.1 updates, then that would make it more likely - though of course not proven - that my installation of HitmanPro Alert was the culprit, rather than any Windows update.

For future reference a restore point shortcut makes it more likely one will be made before program installs

System Restore Point Shortcut - Windows 7 Help Forums

Unfortunately System Restore does not work on my Laptop. I have to make incremental image backups as substitute.
You could take a shot with CCleaner Registry Cleaner. It is one of the safer cleaners and can make a .reg file to put the registry back as it was in case the cleaning munges it. But without any type of backup I don't know what other options there are unless there is a specific forum for that program on the publisher's web site.